Why can I give thumbs down to one answer and not another?

I was looking at a question with a lot of answers, and wanted to give thumbs down to a rude one. The phrase came up "we cannot record your rating right now, try again later" in red. That's odd, says I. So I go to another answer on the same question, also a bad one (but not so rude), and the thumbs... show more I was looking at a question with a lot of answers, and wanted to give thumbs down to a rude one. The phrase came up "we cannot record your rating right now, try again later" in red. That's odd, says I. So I go to another answer on the same question, also a bad one (but not so rude), and the thumbs down rating works. That's even odder, says I. So I go back to the rude one I originally wanted to rate, and hit it again. "Your session has expired. Sign in again." WHAAATTT????
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