No idea. I had the same problem once. Except that in my case it was the Calendar application that kept closing. But that was on a totally borked system. File system corruption, inconsistent packages, you name it. The OP looks like (s)he has some understanding of the Linux command line, so how about - close all applications, open terminal and then:
If you are wondering why not fsck /dev/mmcbl0p2 directly, feel free to try it (it won't break anything, just fail because the device is in use). The dd command will take a while (easily 15 minutes or more), just give it time.