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Just an fyi, sounds like you are aware of the problem, (for the record, it is Http 400, not 500), but may not realize the scope. I've gotten the error on about 7 of my last 10 clicks, and started getting the problem in the morning, about 12 hours ago.
The scope seems to vary dramatically from person to person. My guess is that the backup load balanced server caused the problem. If you just happen to be getting to that one you're going to keep getting the error.