I am having this same issue as well. It started early this morning for me. I closed the program and tried to re-open it. That's when I started getting the "can't validate your credentials" message. I called Lacerte and reported both problems. I can log in again, but am still getting the crash report when I try to move from screen to screen. 

I figured out a work-around. If you have the forms view up on your original monitor, you can then move around in the forms view on your second monitor without getting the crash report.