Powershell error "value can not in the type System Management Automation LanguagePrimitives+InternalPSCustomObject converted"

I am trying to read a txt file with powershell, on only certain characters

$TxtFilePath = "C:\Users\myname\mycode\mydata.txt"
$TxtData = Get-Content $TxtFilePath | ForEach-Object {
    # Ensure the line is long enough before extracting substrings
    $Line = $_.PadRight(138)  # Pad the line to ensure it has at least 138 characters
    $entry = @{
        LastName  = $Line.Substring(18, 40).Trim()  
        FirstName = $Line.Substring(58, 40).Trim()  
        Birthdate = $Line.Substring(128, 10).Trim() 
    }
    [PSCustomObject]$entry
}

that Nth until Nth character is a space for corresponding value (although sometimes for example the name is only 5 character, but chracter 18-58 is prepared for the lastname). When I run that code, the error is """ The value cannot be converted to the type “System.Management.Automation.LanguagePrimitives+InternalPSCustomObject”. Only core types are supported in this language mode. """

And it refers to this line """[PSCustomObject]$entry""" would appreciate any lead

I do expect it can read the txt files according to the rule.

Solution

The error message implies that your session runs in ConstrainedLanguage mode (see the about_Language_Modes help topic).

However, the error message is indicative of a bug, present in Windows PowerShell as well as in PowerShell (Core) 7 as of v7.5.0: You should be able to use a [pscustomobject] cast in order to construct an instance in constrained language mode, given that the type itself (aka [psobject]) is supported in this mode:

See GitHub issue #20767.

Workaround:

Use New-Object rather than a cast to construct your [pscustomobject] instance:

# ...
    $entry = [ordered] @{
        LastName  = $Line.Substring(18, 40).Trim()  
        FirstName = $Line.Substring(58, 40).Trim()  
        Birthdate = $Line.Substring(128, 10).Trim() 
    }
    New-Object pscustomobject -Property $entry
# ...

Note the use of [ordered], i.e. of an ordered hashtable, so as to guarantee that the properties are created in definition order.