John,
That simply just shouldn't be happening. There are a couple of bugs, and AC 4.0 may crash every other day for me. You are talking about the program right and not your client computer?
But, there is something wrong either on your end or on their end. I hate asking these questions but...what version of Vista is it and how much RAM do you have on those PCs? What OS are you running on all the computers AND WHAT TYPE OF COMPUTER, OS AND SPECS DO YOU HAVE THE AC DATABASES ON?
Have you thought about (just for fun) running Win7 on one of the Vista machines?
http://technet.microsoft.com/en-us/evalcenter/dd353205.aspx?ITPID=wcfeed It would be good until March 10, 2010.
