Problem with SendKeys and NT4

I have a visual basic 6 program that uses SendKeys to start an autolisp program inside of AutoCAD. This program works fine on Windows 2000 and AutoCAD 2000. I have a user using Windows NT4 and AutoCAD 2000. The program opens AutoCAD, but you never see any of the Keys sent to the command line and there are no errors. Has anyone experienced anything like this? Solutions?

Thanks in Advance,
Jeff Sanders