If you are using VFP 7.0, you can define the datatype of the parameter. For example, you can say.

LPARAMETERS tcSQL AS Character

I was getting the same error and this worked for me.

>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