"OperationalError: database is locked" appears
Please make sure you have the latest version of Anki installed, as the most likely issue is you have an old version installed.
One other cause of this problem is double-clicking on the Anki icon more than once, which can cause two copies of Anki to try load your data at the same time.
If another copy of Anki does not appear to be running, you can fix this problem by closing Anki in your task manager or restarting your computer.