I had posted this for someone in the old forum, so thought it was worth posting again in case it's useful to anyone.
phpBB 3.0.1 didn't have code change instructions and was solely updated via the auto updater.
While modphpBB3 updated via the auto updater fine, some modded forums and some modphpBB3's that had added more mods had conflict errors while updating from version 3.0.0.
Evil<3 made the code changes in a text format to follow if you wanted to update manually to 3.0.1, so 100% full credit to him for this.
Back up your files before using this, and use at your own risk.