I emailed the broken $10 HIT requester. Here's his reply:
We apologize for your difficulties with the HIT. We had greater uptake than expected all at once and the server could not handle the load. We ask that you submit the HIT before it expires, but still try to complete it using the web link at some point in the next 24 hours. This will naturally space out the people accessing the system and should solve the problem. Please email us your compensation code when you have completed the experiment.
Thanks and very sorry for these difficulties.
Best,
Max
I replied and said I'd returned it because the amount of time and effort I'd have to spent fussing with it and waiting for it to work wouldn't make the $10 worth it.