"Problem with database" error in Safari 5.1
This is a known bug in Safari 5.1 where if you enable Private Browsing in Safari and then quit Safari with it still enabled it can remove the extension database and result in this error the next time you open Safari.
To resolve this, please disable Private Browsing mode before closing the browser. This should reduce the number of times you get the "problem with database" error.
You may also need to restart Safari an additional time (also with Private Browsing disabled).
If are using OS X Lion, you'll need to quit Safari in a manner which bypasses the new application resume feature. To do this, press Option-Command-Q on your keyboard or hold down the Option key when you select the Quit and Close All Windows from the Safari menu.
We have notified Apple and they are aware of this bug. Hopefully, they'll fix it as soon as possible.
