We are using a major piece of software in our company that has been written in VB6 and is too large to migrate. Furthermore we have some old Windows XP PCs that are still being used (no argument, its not my decision). We want to add new functionality to our VB6 program by using VB.NET assemblies. This is working fine for Win Vista and upwards, but XP is behaving erratically.
What I have tried: I've created a Class Library in VB .NET. Made it COM-Visible and registered it for com-interop. I've targeted .NET Framework 4.0 (tried 2.0 also) I've then created a simple class with a simple function for testing purposes:
Imports System.Runtime.InteropServices
<Guid("b98ddfd4-f6bc-40d4-85eb-5bd45c272325")> _
Public Interface Class1_Interface
Function MyFunction(ByVal MyParam As String) As Boolean
End Interface
<Guid("0bbee3db-88e3-4089-adc1-f5a0cf9e1fda")> _
<ClassInterface(ClassInterfaceType.None)>
Public Class Class1 : Implements Class1_Interface
Public Function MyFunction(ByVal MyParam As String) As Boolean Implements Class1_Interface.MyFunction
Try
MyFunction = True
Catch ex As Exception
MyFunction = False
Dim FunctionName As String = System.Reflection.MethodBase.GetCurrentMethod().Name
End Try
End Function
End Class
I've compiled it for X86.
Then I added a reference to it in VB6 and used this simple code in VB6
Private Sub Form_Load()
Dim x As New Class1
MsgBox (x.MyFunction(""))
End Sub
Then I created a manifest and embedded it: mt.exe -managedassemblyname:testDLL.dll -nodependency -out:testDLL.manifest mt.exe -manifest testDLL.manifest -outputresource:testDLL.dll;#1
Then I created a manifest for the exe containing only the most basic information necessary (Type="win32", name, version, processorarchitecture and an assembly block with name, processorarchitecture and version) and an appconfig for the .Net Framework 4 stuff with (I get the same errors with my Framework 2.0 dlls, so this should be irrelevant)
When I execute my VB6 exe in anything higher than XP everything works fine. When I try it on XP I get runtime error '429' Activex component can't create object
The strange thing is, I have a much more complex dll created exactly the same way, just with more functions, using report viewer and sql. Yet this complex dll works fine. The only relevant difference I can find is that it uses a WinForm as a class. Not sure why that should make a difference, but as I said, it is all the same ways of declaring interfaces and classes, creating manifests and whatnot.
I have no idea what to do anymore. I don't know what makes that single DLL work and everything else not.