Carlos,
Have you tried uninstalling and reinstalling VFP 6 (be sure you also add SP3)? It sounds like your run-time libraries may be missing or corrupted.

HTH
Barbara

>I just change a station to Windows NT 4.0 Workstation and when I tray to executing and VFP 6.0 EXE I have the next message:
>This is not a valid application for Window NT. However I can run an .APP whit any trouble.
>
>Note: I have no problems with Windows 95 or 98
>
>TIA