>Ed, what effectively happens if you stick a DoEvents...EndDo around the sleep() call?
>>Sleep() burns no cycles while the API call is in effect, but VFP won't respond to any UI events in the interval that Sleep() is in effect, either, so you have to decide which is more important, responding to UI events or not eating some CPU cycles while idling along between checks for the file arriving.

Nothing; DOEVENTS() is not a loop call, and doesn't refire on an event occurring when it is not actively executing:

DECLARE INTEGER Sleep IN Win32API INTEGER

DO WHILE .T.
   DOEVENTS()  && check for events - one time only
   =Sleep(24*60*60*1000)  &&  do nothing for 24 hours;  VFP gets no UI events
                          &&  if a Key is pressed 12 hours into this, nothing
                          &&  happens until the Sleep() function expires
   *  Do something
ENDDO

Check the docs on DOEVENTS(); it doesn't do what you think it does.