Just in case you're having the same problem as Paynegwynn, whose WoW won't run its video recording feature properly on his Mac for some reason, then here's an explanation.

It turns out that there's some conflict between the video recording feature and a GPU bug. The folks at Blizzard have noted this already and it turns out that they've actually already disabled the option to record videos. Here is Blizz poster Tigerclaw's full explanation:

At present there is a bug in the driver software for that GPU which inhibits our video recording feature (in fact can lead to a crash) - so we disabled it for now on that hardware. However, once an updated driver is released for that machine which addresses that issue, we can post instructions on how to re-enable video recording on that configuration. It's not ideal but this is the best we can do given the bug that we ran into.

Though the solution implemented (meaning the disabling of the recording function) is rather off-putting, it really is the best thing they could do, given that the problem is hardware-based.