Hugo Kornelis (8/12/2010)
Based on visual inspection of the code, you appear to be right about the missing GROUP BY. I'm glad I overlooked that when answering! Luckily, there is no generic "error" answer option, so people will hopefully realise that this is an unintended mistake.
I spotted the missing group by, so assumed that since none of the non-error options could possibly be right, it must be the first option, and that the error was being raised before it got as far as the 'no group by' error. 🙁