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This is to prevent "voting rings" using new accounts. It is a small measure of activity. All it would have taken from you was 15 rep,

1 Upvoted Answer (+10) and 1 Upvoted Question (+5) or 1 Question Upvoted (3 times) (+15) or 3 Upvoted Questions (+15)

(It is actually 14, since you start off with 1 rep)

That is really not a lot of activity/work needed from an individual.

Most likely a next user would have seen the answer on rails and voted by now.

The weird thing is how it doesn't tell you that you can't upvote until you try to do it.

It tells you in the FAQ. http://stackoverflow.com/faq#reputation

I meant that it is surprising that they don't hide the controls that you can't use.

Hey, let’s all downvote alexsherrick and tell him he’s an idiot for not understanding site policy instead of recognizing that he is pointing out an undesirable effect of that policy!