…and your syslog says something like:
30.06.12 10:20:41,526 Beamer: Unable to load nib file: MainMenu, exiting 30.06.12 10:20:41,528 com.apple.launchd.peruser.501: ([0x0-0x2d02d].com.tupil.beamer) Exited with code: 1
….then you might be using a little tool called Disk Doctor to free up your disk space. If you’ve configured Disk Doctor to remove (purportedly) unnecessary language files it will kill your Beamer installation.
The solution is simple: re-download Beamer App and copy it over the old one inside your applications directory, overriding existing files. Uncheck that option in Disk Doctor and Beamer should be running smoothly as ever.