This Bible contradiction is from the Skeptic's Annotated Bible.
In the twelfth year of Joram.
2 Kings 8:25 View context
In the twelfth year of Joram the son of Ahab king of Israel did Ahaziah the son of Jehoram king of Judah begin to reign.
In the eleventh year of Joram.
2 Kings 9:29 View context
And in the eleventh year of Joram the son of Ahab began Ahaziah to reign over Judah.