Had a problem where OF desktop was stuck during a sync, which would never complete. The error message said "Unable to authenticate with WebDAV server." Resetting OF's sync preferences would not re-prompt for password, so I deleted the MobileMe password entry from KeyChain (which did have the correct password). Although this caused OF to re-prompt for the password, it still wouldn't sync.
Guessed (hoped?) that re-running the CoalesceDatabase script might fix things. Did this, re-named the MobileMe folder to OmniFocus.ofocus-OLD, and (for good measure) re-deleted the KeyChain MobileMe entry. Once OF was restarted, and its Sync Preferences verified, it synced immediately. All is happiness, again. :)
Guessed (hoped?) that re-running the CoalesceDatabase script might fix things. Did this, re-named the MobileMe folder to OmniFocus.ofocus-OLD, and (for good measure) re-deleted the KeyChain MobileMe entry. Once OF was restarted, and its Sync Preferences verified, it synced immediately. All is happiness, again. :)