We ran into a similar issue because we were using a third-party backup tool (I
don't know what it's called, sorry! I am a code monkey not a server admin.) What
was happening was the backup program would lock the database to a read-only
state to do the backup (you wouldn't want it changing anything!) but it was not
properly UNLOCKING the database again. When we would come in Monday mornings we
would not be able to do anything that would cause commits to the database. We
could read (SELECT) just fine...but, no CREATE, UPDATE, or DELETE.