Messager has error and won't open

Safe Boot from the HD, (holding Shift key down at bootup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.

Well, you'd need a Time Machine Backup or to reinstall the whole OS... do you have a backup?

To find out if it's system wide or user specific, try this...

Open System Preferences>Users & Groups, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.

Does it work in the new account?

Great to hear. :)