I sometimes find both sites timing out if I refresh a page and pick up (or drop) a wifi connection. It seems if you start the process on 3G you have to finish it on 3G. Usually killing the app (or Safari) in the multitask bar sorts the problem out.
Occasionally, it doesn't. In a case like this I refresh Mail to force an Internet connection, and that usually does the trick.
Sent from my iPad 4 HD mini