I have an Error 91 only on 3 workstations since upgrading to v9.1.0. I decided to delve a little deeper into this error and this is what I discovered for my situation:

I have 7 workstations. There are 3 exam room, 1 personal office, and 3 office staff. I have a bad habit of log onto my personal office workstation, then walk away and AC times out. I then go to an exam room, log on and see a patient, then log off. If I then go back to same exam room workstations that I have previously logged onto while my personal office workstation is still "timed out" from previous log in, Error 91 occurs, AC crashes (on the exam room workstation) and have to re-start the AC program. This only occurs on the exam room workstations since I never log on to AC on my office staff AC workstations. Now, If I log off personal workstation, then use AC as regular in the Exam rooms and log off/on, then no error 91. Therefore, to me this is a bug. Yes, I should be logging off manually before walking away from any workstation. And if I follow that practice, then no error 91.

I thought this was a .NET problem and had support log onto my network server and workstations and they could not find a problem. I then fresh installed windows 7 sp1 and still got problem. Then I fresh installed windows 10 and still got same error. Therefore, it is not a windows or AC installation problem but is an actual bug in how the log on process is handled, if a previous log in is timed out on another workstation. This never happened with any other prior version of AC I used.

Just wanted to get this out there and see if anyone else able to replicate this error. Or has similar experience.