Error while posting

I get the following error whilst posting:

WordPress database error: [Duplicate entry '0' for key 1]
INSERT INTO wp_usermeta ( user_id, meta_key, meta_value ) VALUES ( '1', 'wp_autosave_draft_ids', 'a:1:{i:-1190814115;i:28;}' )

It should be noted that even though I get the error, the post is still published.