Gmiles, Since the function declaration uses "As Long" as the datatype, try using numeric datatypes in LabVIEW. When you run the Visual Basic example, what value is the actual number value that it is passing the .dll? Also, since the FileName is forced to a pointer in Visual Basic, try the string datatype in LabVIEW with the C string pointer format first, and then the other formats. Are you using the Standard (WINAPI) calling conventions? If none of these different options help, please let us know what error code you are getting.