it tried to replicate the problem in our test environment, but I could not produce any BSOD or reboot. When you receive a BSOD, Windows creates a Minidump of the crash. Could you please send me those dump files at our email at contact at boxcryptor.com? They are located in C:\Windows\Minidump.
If you do not have any sensitive information in the exported TMP preferences file, it could be helpful if you could send me this file also.
PS: You could also start BoxCryptor with the /debug parameter (Start -> "BoxCryptor.exe /debug") and replicate the reboot. BoxCryptor will then create a log file on your Desktop (BoxCryptor.log) which could help to find the problem.