Why are my Google AppEngine instances crashing with 'error code 121'?

Question

I have been running a java high-replication web application on Google AppEngine for some time now. About two days ago - basically out of nowhere - a lot of requests began to fai

Answer 1

Have not seen anything for sure about this from Google. They are often shy to explain such issues. One of the threads do mention datastore migration. See if that helps;

http://code.google.com/p/googleappengine/issues/detail?id=7022