Technically both the "correct" answer and the answer marked "No rows returned, conversion error on query 3" are correct. It depends on how the Query Analyzer and query engine process the query. It could choose to multi-thread it and the first item it examined could have the error, thus no rows returned. Additionally, the table is a Temp Table with no indexes (Heap) and add in the fact that query returned is not garaunteed an order unless an explicit order by is stated. I have run into many instances where I tried to filter out by isdate(xyz) = 1 only to have the query fail because it didn't process in the order I thought it should.