The pop up message is Apport, Ubuntu's error reporting program. As @mdooley says, it's caught these applications (nautilus, shotwell, udisksd) from crashing. Sometimes it's a crash that happened in the background but auto-restarted.
They normally contain a "core dump" which is useful for a developer to know where in the code it crashed, so it's probably not worth your time researching unless you can easily reproduce the crash. If it's already reported using "Report problem..." then it should be on Launchpad ready for fixing in a future update.
Instead of clearing /var/crash/, it might be worth disabling Apport so it doesn't create crash files or show the error message: