We have been working on an ODK 2.0 project for a while and had originally set up an Aggregate server on Google App Engine. We were just adding another tablet to our workflow today, and when we were at the step to set up the link to the server in ODK services, after entering the url, user name, and passwords, when we got to verify user permissions, then got the error "Internal Server Error (out of quota?)"
Took us a while to figure out what the error was (everything is happy now) but I wanted to post this in case anyone else has the same problem, since when we googled "Internal Server Error (out of quota?)" there were zero results.
It turns out we had downloaded rev214 of the tools to the tablet. We had been working with rev208 of the tools and the corresponding version of aggregate. "Internal Server Error (out of quota?)" translated to "You have different versions of the software on your tablet and server." When deleted the rev214 and downloaded rev208 to the tablet instead, everything worked.
So FYI for anyone who runs into the same problem--and if the error message is something coming from ODK not App Engine, a suggestion for a more informative error message