I've been getting this same error for several weeks on both my iPad and iPod Touch. And lots of other problems like syncing not working, duplicates of messages, messages with corrupt attachments, etc. For this reason I have given up trying to use email on these devices. Waste of time. Lots of people have been having the same issues, but Apple have been quick to delete a lot of the threads from it's own support site.
When I phoned Apple support, they first told me the unthinkable - that I should try reseting my devices and doing a permissions repair on my Mac. I followed those instructions, and much to my surprise everything was just as broken as it was before.
When I phoned Apple support a second time, I then got told that "Apple don't provide support for third party services". It seems like Apples customer service has hit a new low. Not what you expect after spending £399 on an iPad, plus £59 AppleCare.