Interop DLL returning member not found

OK, this is a shot in the dark as I'm at my wits end. I have two third-party DLLs that work great in VB6, but not so much in VB.NET or C#.

In VB6, the below works just fine:

Dim oApplication As Object
Dim oSession As Object
Dim vRetCode As Variant

Set oApplication = CreateObject("OAPPLICA.OAPPLICA")
Set oSession = CreateObject("OSESSION.OSESSION")

oApplication.PROGRAMDRIVE = "\\dev\data\"
oApplication.WORKAREADRIVE = "\\dev\data\workarea\"
oApplication.DATADRIVE = "\\dev\data\"
oApplication.IMAGEDRIVE = "\\dev\data\image\"

oSession.MYAPPLICATION = oApplication
vRetCode = oSession.LOGIN("USER1", "PASSWORD1") 'Returns zero if successful

MsgBox (vRetCode)

When I run this exact same set of code in VB.NET I get "Member not found. (Exception from HRESULT: 0x80020003 (DISP_E_MEMBERNOTFOUND))" on the "oSession.MYAPPLICATION = oApplication" line.

I've tried doing early binding as well in both VB.NET and C#, but eventually end up with the same error on a different line. I get the same error for the below on the "oApplication.set_PROGRAMDRIVE("\\dev\lifepro\data\");" line.

private OAPPLICA.OAPPLICA oApplication = new OAPPLICA.OAPPLICA();
private OSESSION.OSESSION oSession = new OSESSION.OSESSION();
Int64 iReturnCode;

oApplication.set_PROGRAMDRIVE("\\\\dev\\data\\");
oApplication.set_WORKAREADRIVE("\\\\dev\\data\\workarea\\");
oApplication.set_DATADRIVE("\\\\dev\\data\\");
oApplication.set_IMAGEDRIVE("\\\\dev\\data\\image");

m_oSession.set_MYAPPLICATION(m_oApplication);
iReturnCode = Convert.ToInt64(m_oSession.LOGIN("USER1", "PASSWORD1"));

As stated earlier, the two DLLs (OAPPLICA.dll and OSESSION.dll) are third-party and allow an entry point into a third-party legacy system. Since it's legacy I don't have access to the third-party anymore, I've just been tasked with trying to prototype converting an existing Windows VB6 application into an .NET web application. My hunch is .NET is having an issue interpreting the interop DLL for the two COM objects, but I have been unable to find anything to point me in a direction.

My guess is that this code would run fine in a WinForms app, have you tried that?

VB6, and most COM components designed for use with VB6, are going to require you to run on an STA thread to work properly. Your web code is likely running on at MTA thread.