For those Google AdWords API developers, you should be aware that currently any requests sent over the SOAP protocol to the API Sandbox will return an error.
A Google Groups thread has one developer complaining and an official Google representative confirming the issue. Jeff Posnick from the AdWords API Team said:
I can confirm that the Sandbox is returning "internal error" SOAP faults for all requests right now. I've let the engineering team know and they're investigating the root cause.
Typically, sandbox errors are not fixed as quickly as production errors. But since the API is returning errors for all SOAP requests, I have a feeling this will be fixed faster than an normal sandbox bug.
Forum discussion at Google Groups.