I have VFP single threaded dll that looks up file locations on my system.
In VFP, I use it like

oFF = CREATEOBJECT('FindFile.FindFile')
cFilename = oFF.m_FindFile('filetoken')

For .net, I created a runtime-callable wrapper with

tlbimp Findfile.tlb /out: RCW_FindFile.dll /Keyfile:keypair

I added the RCW as a reference in my project and added the following in a button_click handler.

Dim FindFile AS New RCW_FindFile.findfile()  'VS added the () automatically
Dim strToken AS String
Dim strFile AS String
strToken =  "ClaimsInProgress"
strFile = FindFile.FindFile(strToken)

Whenever I run this, .Net throws an exception

An unhandled exception of type 'System.InvalidCastException' occurred in microsoft.visualbasic.dll

Additional information: Cast from string "ClaimsInProgress" to type 'Integer' is not valid.

If I pass no argument to m_FindFile method, the appropriate error string message is returned. Whenever I pass an argument, I get the exception. Does anybody know whats going on? TIA