To put what ScratSkinner said another way, go to ~/Library/Preferences/Mission Computer and delete any files in there. You should find only the file you were trying to edit. Mission Computer keeps a log of what was open in that folder so if it crashes it can try and reopen those files for you upon reboot. Unfortunately, if said file is the reason MC crashed in the first place, this causes it to not open as the file continues to crash. Deleting the files in that folder will allow MC to start up again.
As for certain resources causing MC to crash when you try to edit it, I've had this same issue a few times myself. There doesn't seem to be any rhyme or reason to it as I can get the resources that cause the issue to open if I keep trying. This will sound like superstition, but if you open a different resource type and then go back to the one that caused the crash, sometimes it will open instead of crashing. If that doesn't work, try opening another resource of the same type instead of the one that caused the crash. In your case where clicking on a specific resource type in the sidebar causes the crash, click on a different type first, then go back to the one you want. Again, this feels like suppression, but it works for me and I'm not certain why.