1004 error while creating and saving workbook in excel vba

I have a function that gets a name for a new workbook, tries to open that workbook in the current folder and, if it can't do this, create a new workbook and save it in the current folder (and I am trying to save it with the name for the file, passed to the function). Looks like the workbook is created, as it opens (but with name "pasta11", which isn't what I expected) but it isn't saved anywhere.

Public Function SaveNewWorkbookToRelativePath(nameOfNewFile As String)
    Dim relativePath As String
    relativePath = ThisWorkbook.Path & "\" & nameOfNewFile
    On Error GoTo NoSheetHandler
    Workbooks.Open (relativePath)
    Exit Function
NoSheetHandler:
    Workbooks.Add.SaveAs Filename = relativePath, FileFormat = 52
End Function

The error is Runtime error 1004: application or object defined error.

Solution

Open or Create & Save a Workbook

A Test

Sub OpenMewTEST()
    OpenMew "Test1"
End Sub

The Method (Sub)

Sub OpenMew(ByVal BaseName As String)
    Const PROC_TITLE As String = "Open Macro-Enabled Workbook"
    On Error GoTo ClearError
    
    Const FILE_EXTENSION As String = ".xlsm" ' fixed
    
    Dim fName As String: fName = BaseName
    
    If StrComp(Right(fName, Len(FILE_EXTENSION)), FILE_EXTENSION, _
            vbTextCompare) <> 0 Then
        fName = fName & FILE_EXTENSION
    End If
       
    Dim wb As Workbook:
    On Error Resume Next
        Set wb = Workbooks(fName)
    On Error GoTo ClearError
    
    If Not wb Is Nothing Then
        MsgBox "A workbook named """ & fName & """ is already open.", _
            vbExclamation, PROC_TITLE
        Exit Sub
    End If
    
    Dim fPath As String:
    fPath = ThisWorkbook.Path & Application.PathSeparator & fName
    
    Dim CheckName As String: CheckName = Dir(fPath)
    
    If Len(CheckName) = 0 Then
        
        Set wb = Workbooks.Add(xlWBATWorksheet) ' single worksheet
        
        Dim ErrNumber As Long, ErrDescription As String
    
        On Error Resume Next
            wb.SaveAs fPath, xlOpenXMLWorkbookMacroEnabled ' 52
            ErrNumber = Err.Number
            ErrDescription = Err.Description
        On Error GoTo ClearError
        
        If ErrNumber = 0 Then
            MsgBox "Workbook """ & fName & """ created and saved.", _
                vbInformation, PROC_TITLE
        Else
            If Not wb Is Nothing Then
                wb.Close SaveChanges:=False
            End If
            MsgBox "Run-time error '" & ErrNumber & "':" & vbLf & vbLf _
                & ErrDescription & vbLf & vbLf & "Could not save as """ _
                & fPath & """.", vbCritical, PROC_TITLE
        End If
    
    Else
        
        Workbooks.Open fPath
        MsgBox "Workbook """ & fName & """ opened.", _
            vbInformation, PROC_TITLE
    
    End If
    
ProcExit:
    Exit Sub
ClearError:
    MsgBox "Run-time error '" & Err.Number & "':" & vbLf & vbLf _
        & Err.Description, vbCritical, PROC_TITLE
    Resume ProcExit
End Sub