How To: Fix a Glitch in Which Mail Won't Open

Today I did the upgrades for iDVD, iMovie, iPhoto and iSight. Later I shut down my computer and when I turned it back on, Mail wouldn't open. When I clicked on the Mail icon in the Dock, it would bounce for a while but then just stop bouncing and nothing more would happen.

I tried to open in it in the subfolder in the Applications folder in which I had put it. It didn't work.

So then I repaired permissions using Disk Utility and moved Mail to the Applications folder. I tried to open it in the Dock and it didn't work. But then I tried to open it in the folder and it did work.