>I use Groupwise Object functions to open a new mail window. I call a function that acepts two strings for parameters. It works in one computer, but it gives an error message in another computer. The error message is "Function argument value, type or count is invalid".
>When I use a simple VB program to do the same thing, it works in every computer.
>So I think it is not dll problem (it works in another language).
>Any suggestion is greatly appreciated.

Any chance that either one or both parameters are empty?

If the VFP DLL is not checking the parameters for Empty() or even PCount(), this error will pop up. As a test, write the Transform()ed parameters to a text file in your function before doing any processing.