Got this error message on Mac OS X Yosemite when opening the Messages app:
There was a problem with Messages.
You need to quit and open Messages again
Fix this by:
1. Open contacts app
2. Disable all the accounts you have there (iCloud, Google, etc..)
3. Now you have no contacts in your contacts list
4. Open Messages app
Now the Mac OS X Yosemite 10.10 Messages App works!