There is a known issue with MR that occurs after applying Security Update for Microsoft Windows (KB3059317), that was released in June 2015. If you try to export reports or click File | Open, MR will crash. This has been fixed in CU13 (2.12.13001).
If you are not able to upgrade to CU13 immediately, you can work around this by using the keyboard to navigate the windows, instead of using mouse clicks.