MSAccess.SysCmd converting old mdb to accdb, in vb.net vs2019 - vb.net

Question

I'm having issues converting an old access mdb to the newer format (2007) accdb.
In the past I have used the following code, that works:
' Delete the resultant accdb just in case
File.Delete("C:\temp\TheTargetDB.accdb")
Dim oAccess = CreateObject("Access.Application")
Dim ret = oAccess.SysCmd(603, "C:\temp\TheSourceDB.mdb", "C:\temp\TheTargetDB.accdb")
oAccess.quit()
oAccess = Nothing
If ret = 0 Then
MsgBox("DID NOT CONVERT")
Exit Sub
End If
However, I've tried using it with variables and this doesn't work:
Dim SourceDBName As String = "C:\temp\TheSourceDB.mdb"
Dim TargetDBName As String = "C:\temp\TheTargetDB.accdb"
' Delete the resultant accdb just in case
File.Delete(TargetDBName)
Dim oAccess = CreateObject("Access.Application")
Dim ret = oAccess.SysCmd(603, SourceDBName, TargetDBName)
oAccess.quit()
oAccess = Nothing
If ret = 0 Then
MsgBox("DID NOT CONVERT")
Exit Sub
End If
Is there anything special about the SysCmd that I'm not aware of?

Answer 1

After many hours of pulling my hair out, I stumbled onto the answer while reviewing the Microsoft Doc article: MS Access SysCmd method
The argument types for the source and target are the old 'variant' data type.
I decided to modify my code to cast the string variables to the 'Object' type:
Dim ret = oAccess.SysCmd(603, CObj(SourceDBName), CObj(TargetDBName))
vs2019 says the cast is redundant, but guess what? - it worked!
I hope this is useful to anyone in a similar situation.
Cheers
Andrew