For those of you like me who can't even test this amazing SMS feature because the app crashes on start... Back up all data. Quit Messages if it’s running. Step 1 Hold down the option key and select Go ▹ Library from the Finder menu bar. Delete the following items from the Library folder (sometimes it may not exist): Caches/com.apple.Messages Leave the Library folder open. Try Messages again. If it works now, stop here. Close the Library folder. Step 2 If you still have problems, quit Messages again. Go back to the Finder and move the following item from the open /Library/ folder to the Desktop: Messages (Note: you are not moving the Messages application. You’re moving a folder named “Messages.”) Test. If Messages now works, delete the Messages folder on the Desktop. Otherwise, quit Messages again. Put back the folder you moved, overwriting the newer one that may have been created in its place, and continue. Step 3 In the Preferences subfolder, there may be several files having names that begin with "com.apple.iChat". Move them all to the Desktop. Also in the Preferences folder, there's a subfolder named "ByHost". Open it and do the same thing. Test again. This time Messages should perform normally, but your settings will be lost. You may be able to put back some of the files you moved to the Desktop in this step. Relaunch and test after each one. Eventually you should find one or more that causes Messages to malfunction. Delete those files and recreate whatever settings they contained. If the issue is still not resolved, quit Messages again and put all the items you moved to the Desktop back where they were. You don’t need to replace the files you deleted in step 1. Stop here and post again. If you later decide that you don’t like the results of steps 2 and 3, you can undo them completely by quitting Messages and restoring the items you deleted in those steps from your backup. Source : https://discussions.apple.com/thread/4600732 Although I spoke too fast. Now it says my database is being upgraded, but nothing seems to be happening. The progress bar is stuck at 0. I guess I found half of the solution, does anybody else have the other half ?