RESOLVED: If you've set any of your videos to only display comments after you've approved them, you currently can't approve comments. When you click the "Approve" link next to any pending comments, you'll receive an error message. We're working to resolve this problem as quickly as possible, and will update you when it's been fixed.
Update (7/26/2007, 9:23 PM PDT):
This has been fixed. You can now approve video comments as usual.