Our app has been running for years since FP 2.6

Suddenly (VFP 6.0 version) over the past few weeks two users have called saying when they click a button.
(DO FORM )

the whole system freezes...

3 users at the same company with the same software.
2 this happens on 5-10 times a day.

but not always 1 user it never happens....

Running Windows 95 32 mb and 40mb.
HP LaserJet 4000 printer drivers....

Video card???

Anyone experienced this...!!!

Thanks