Access 2010 Audit Trail on SubForms

I am having trouble getting the code I found for an audit trail to work with sub forms. The origninal code is from http://www.fontstuff.com/access/acctut21.htm. I would rather stick to this code than using Allen Browne's code http://allenbrowne.com/appaudit.html. It seems to be a problem with Screen.ActiveForm.Controls. I have read that this does not work with sub forms. Is there a way I can alter this to audit a sub form in my database?

When I record the data in the sub form, I get the following error: Microsoft can't find the field "CalSubID" referred to in your expression."

In a module I have this code (this is just part of it that I think is having issues):

Sub AuditChanges(IDField As String, UserAction As String)
On Error GoTo AuditChanges_Err
Dim cnn As ADODB.Connection
Dim rst As ADODB.Recordset
Dim ctl As Control
Dim datTimeCheck As Date
Dim strUserID As String
Set cnn = CurrentProject.Connection
Set rst = New ADODB.Recordset
rst.Open "SELECT * FROM tblAuditTrail", cnn, adOpenDynamic, adLockOptimistic
datTimeCheck = Now()
strUserID = Forms!Login!cboUser.Column(1)
Select Case UserAction
    Case "EDIT"
        For Each ctl In Screen.ActiveForm.Controls
            If ctl.Tag = "Audit" Then
                If Nz(ctl.Value) <> Nz(ctl.OldValue) Then
                    With rst
                        .AddNew
                        ![DateTime] = datTimeCheck
                        ![UserName] = strUserID
                        ![FormName] = Screen.ActiveForm.Name
                        ![Action] = UserAction
                        ![RecordID] = Screen.ActiveForm.Controls(IDField).Value
                        ![FieldName] = ctl.ControlSource
                        ![OldValue] = ctl.OldValue
                        ![NewValue] = ctl.Value
                        .Update
                    End With
                End If
            End If
        Next ctl
    Case Else
        With rst
            .AddNew
            ![DateTime] = datTimeCheck
            ![UserName] = strUserID
            ![FormName] = Screen.ActiveForm.Name
            ![Action] = UserAction
            ![RecordID] = Screen.ActiveForm.Controls(IDField).Value
            .Update
        End With
End Select
AuditChanges_Exit:
On Error Resume Next
rst.Close
cnn.Close
Set rst = Nothing
Set cnn = Nothing
Exit Sub
AuditChanges_Err:
MsgBox Err.Description, vbCritical, "ERROR!"
Resume AuditChanges_Exit
End Sub

Then in my "before update" and "AfterDelConfirm" events for the subform I have (where "CalSubID" is the PK for the subform and this is what the main module code uses to track the changes):

-----------------------------------------------------------------------
Private Sub Form_BeforeUpdate(Cancel As Integer)
If Me.NewRecord Then
    Call AuditChanges("CalSubID", "NEW")
Else
    Call AuditChanges("CalSubID", "EDIT")
End If
End Sub
-----------------------------------------------------------------------
Private Sub Form_AfterDelConfirm(Status As Integer)
If Status = acDeleteOK Then Call AuditChanges("CalSubID", "DELETE")
End Sub
-----------------------------------------------------------------------

Modified Code:

Sub AuditChanges(IDField As String, UserAction As String)
On Error GoTo AuditChanges_Err
Dim cnn As ADODB.Connection
Dim rst As ADODB.Recordset
Dim ctl As Control
Dim datTimeCheck As Date
Dim strUserID As String

'added code
Dim SubFormName As String

Set cnn = CurrentProject.Connection
Set rst = New ADODB.Recordset
rst.Open "SELECT * FROM tblAuditTrail", cnn, adOpenDynamic, adLockOptimistic
datTimeCheck = Now()
strUserID = Forms!Login!cboUser.Column(1)

'msgbox to display name (just for now to test code)
MsgBox (" " & Screen.ActiveForm.Name & " ")

'IF THEN statement to check if user is using form with subform
If Screen.ActiveForm.Name = "Cal Form" Then
SubFormName = "Cal Form Sub"

    Select Case UserAction
    Case "EDIT"
        For Each ctl In Screen.ActiveForm
            If ctl.ControlType = acSubform Then
            SubFormName = ctl.Name
            If ctl.Tag = "Audit" Then
                If Nz(ctl.Value) <> Nz(ctl.OldValue) Then
                    With rst
                        .AddNew
                        ![DateTime] = datTimeCheck
                        ![UserName] = strUserID
                        ![FormName] = SubFormName
                        ![Action] = UserAction
                        ![RecordID] = Forms![Screen.ActiveForm.Name]![SubFormName].Form![IDField].Value
                        ![FieldName] = ctl.ControlSource
                        ![OldValue] = ctl.OldValue
                        ![NewValue] = ctl.Value
                        .Update
                    End With
                End If
            End If
'Getting error message at the --Next ctl-- line below, "next without for" message....
        Next ctl
    Case Else
        With rst
            .AddNew
            ![DateTime] = datTimeCheck
            ![UserName] = strUserID
            ![FormName] = SubFormName
            ![Action] = UserAction
            ![RecordID] = Forms![Screen.ActiveForm.Name]![SubFormName].Form![IDField].Value
            .Update
        End With
        Set ctl = Nothing
End Select

Else

Select Case UserAction
    Case "EDIT"
        For Each ctl In Screen.ActiveForm.Controls
            If ctl.Tag = "Audit" Then
                If Nz(ctl.Value) <> Nz(ctl.OldValue) Then
                    With rst
                        .AddNew
                        ![DateTime] = datTimeCheck
                        ![UserName] = strUserID
                        ![FormName] = Screen.ActiveForm.Name
                        ![Action] = UserAction
                        ![RecordID] = Screen.ActiveForm.Controls(IDField).Value
                        ![FieldName] = ctl.ControlSource
                        ![OldValue] = ctl.OldValue
                        ![NewValue] = ctl.Value
                        .Update
                    End With
                End If
            End If
        Next ctl
    Case Else
        With rst
            .AddNew
            ![DateTime] = datTimeCheck
            ![UserName] = strUserID
            ![FormName] = Screen.ActiveForm.Name
            ![Action] = UserAction
            ![RecordID] = Screen.ActiveForm.Controls(IDField).Value
            .Update
        End With
End Select


AuditChanges_Exit:
On Error Resume Next
rst.Close
cnn.Close
Set rst = Nothing
Set cnn = Nothing
Exit Sub
AuditChanges_Err:
MsgBox Err.Description, vbCritical, "ERROR!"
Resume AuditChanges_Exit
End Sub

I'm presuming your error is with the line (it would help if you would verify):

![RecordID] = Screen.ActiveForm.Controls(IDField).Value

The issue as you've stated is that you can't access subform controls this way but must reference in this manner:

![RecordID] = Forms![main form name]![subform control name].Form![control name].Value

In your case, you need to first find the subform control name (presuming you only have 1 subform)

' Visit each control on the form
Dim ctl As Control
Dim SubFormName as string
SubFormName = ""
For Each ctl In Screen.ActiveForm
    If ctl.ControlType = acSubform Then
        SubFormName = ctl.Name
        exit for
    End If
Next ctl
Set ctl = Nothing

Now in your code when setting RecordID, you can do it like this:

' you should check that SubFormName is not empty before this next line...
![RecordID] = Forms![Screen.ActiveForm.Name]![SubformName].Form![IDField].Value

I have not tested this and I'm a bit rusty on Access, so take the concept and fix the syntax.

** UPDATE** - Here is the code I would try with the new information you have provided. I am presuming that the controls (e.g. the one with ctl.Tag = "Audit") are all on the subform

Sub AuditChanges(IDField As String, UserAction As String)
On Error GoTo AuditChanges_Err
Dim cnn As ADODB.Connection
Dim rst As ADODB.Recordset
Dim ctl As Control
Dim datTimeCheck As Date
Dim strUserID As String

'added code
Dim SubFormName As String

Set cnn = CurrentProject.Connection
Set rst = New ADODB.Recordset
rst.Open "SELECT * FROM tblAuditTrail", cnn, adOpenDynamic, adLockOptimistic
datTimeCheck = Now()
strUserID = Forms!Login!cboUser.Column(1)

'msgbox to display name (just for now to test code)
MsgBox (" " & Screen.ActiveForm.Name & " ")

'IF THEN statement to check if user is using form with subform
If Screen.ActiveForm.Name = "Cal Form" Then
  SubFormName = "Cal Form Sub"

    Select Case UserAction
    Case "EDIT"
        For Each ctl In Forms![Cal Form]![Cal Form Sub].Form
            If ctl.Tag = "Audit" Then
                If Nz(ctl.Value) <> Nz(ctl.OldValue) Then
                    With rst
                        .AddNew
                        ![DateTime] = datTimeCheck
                        ![UserName] = strUserID
                        ![FormName] = SubFormName
                        ![Action] = UserAction
                        ![RecordID] = Forms![Cal Form]![Cal Form Sub].Form![IDField].Value
                        ![FieldName] = ctl.ControlSource
                        ![OldValue] = ctl.OldValue
                        ![NewValue] = ctl.Value
                        .Update
                    End With
                End If
            End If
        Next ctl
    Case Else
        With rst
            .AddNew
            ![DateTime] = datTimeCheck
            ![UserName] = strUserID
            ![FormName] = SubFormName
            ![Action] = UserAction
            ![RecordID] = Forms![Cal Form]![Cal Form Sub].Form![IDField].Value
            .Update
        End With
        Set ctl = Nothing
    End Select

Else

  Select Case UserAction
      Case "EDIT"
          For Each ctl In Screen.ActiveForm.Controls
              If ctl.Tag = "Audit" Then
                  If Nz(ctl.Value) <> Nz(ctl.OldValue) Then
                      With rst
                          .AddNew
                          ![DateTime] = datTimeCheck
                          ![UserName] = strUserID
                          ![FormName] = Screen.ActiveForm.Name
                          ![Action] = UserAction
                          ![RecordID] = Screen.ActiveForm.Controls(IDField).Value
                          ![FieldName] = ctl.ControlSource
                          ![OldValue] = ctl.OldValue
                          ![NewValue] = ctl.Value
                          .Update
                      End With
                  End If
              End If
          Next ctl
      Case Else
          With rst
              .AddNew
              ![DateTime] = datTimeCheck
              ![UserName] = strUserID
              ![FormName] = Screen.ActiveForm.Name
              ![Action] = UserAction
              ![RecordID] = Screen.ActiveForm.Controls(IDField).Value
              .Update
          End With
  End Select
End If

AuditChanges_Exit:
    On Error Resume Next
    rst.Close
    cnn.Close
    Set rst = Nothing
    Set cnn = Nothing
    Exit Sub
AuditChanges_Err:
    MsgBox Err.Description, vbCritical, "ERROR!"
    Resume AuditChanges_Exit
    End Sub