I have had the exact same problem and error message. To add to this, the response actually hits the e-mail address set up for responses, but still gives the error message. However, it does not hit the file also set up to receive and track the responses.I followed the advice previously given and re-built the pages from scratch. No copying and pasting any part, I re-keyed the entire page. When I re-published, and previewed, it worked. BUT, when I went out and tested on the actual live page, again the same error message.
Additional information on this problem is my company, since it has several locations around the world, uses what they call a "Cluster Format" for the USA servers. (And does anyone other than me find that term amusing) Each location has a publishing server, then said servers update to the "live" server every two hours.
This problem is preventing us from announcing the newly formatted site to our 2000+ hotels and users. So other than taking a sledgehammer to my computer or throwing it under the next freight train, I am at the end of my rope.