Contradiction with 2 Samuel 24:18
2 Samuel 24:18 describes the same event, but there are differences in details and context leading up to this point, particularly regarding who incited David to take a census, which could be seen as contradictory to some interpretations of 1 Chronicles 21.
2 Samuel 24:18: And Gad came that day to David, and said unto him, Go up, rear an altar unto the LORD in the threshingfloor of Araunah the Jebusite. [Araunah: Heb. Araniah]