GAE Mysterious Quota Limit

Question

I have a Google App Engine app which currently displays:

Over Quota

This application is temporarily over its serving quota. Please try again later.

I have a billed account. When I check my quotas, I am well under all limits. I have about 10,000 tasks sitting in the queue waiting to be processed - but even that is well under the 1,000,000,000 limit.

I have no idea how to debug this as all I get is the message that I'm over quota which, according to my quota stats, is not true.

Here is a dump of the quota stats (sorry about the formatting):

http://paste2.org/p/2091412

Answer 1

It is because of the frontend instance hours eaten up by the task queue. I thought I had configured the app to use one backend instance, but apparently not: GAE: Queues, Quotas and backend instances