Hi Virusim;

>They are looping to check for new files only and then
process them. My application all will be running 7 days 24 hours.

Is very important for us know how exactly are you doing this.. Can you pub. the code ? If you run your app 24h per day you may do this using a looping based on the TIMER object.

>recently it often give errors of 'illegal operation...' on
one of the program, on clicking okay, it will cause all other 2 program
to exit too.

'illegal operation...' happens too when the computer/Win98se does not have enough resources.

>Finally, after a few day, I notice that the system time is slow down
by at least 15 minutes. could using DOEVENT() function cause it to slow
down ?

Depends on how many operations you have in your events.

CLAUDIO