Just in case, please try to always launch the Forex Tester program as administrator (right-click -> run as administrator).
This can help to fix the issue with access violations.
If this issue happens again please send a bugreport.txt file that you can find in the Forex Tester 4 folder. This file contains all the info about occurred bugs.
Please also send the debug.log and ForexTester.log files that you will find in the <ForexTester4>\LOGS folder.
You can send these files to our email email@example.com
Our developers will review these logs and they will try to find a reason of the issue.