This API error indicates that there was a problem processing your query request. This can occur if you make too many bad queries in a short period of time, or if you use use up your quota for the day. In some cases, it may indicate that the server was too busy to process your request (usually for a very large query).
If you get any error from a query, check to see that your query is valid instead of simply trying over and over. Too many attempts will cause even good queries to get blocked in this way.