I had the same problem last week. There's a webinar you can watch that explains Name mapping in details and how to debug those errors, here's the link.
the problem is that your two textboxes have the same name, so you have to make them out by something else than the name (the index is nice, or you could seperate them by their tag.. just try finding what's different between the two, and if you're still in developement phase, you could ask your devs to give them a different name)
follow the link on your test complete start page to see recorded webinars
