This looks like a duplicate of Throttle violation after 300 calls but this one is reported as fixed in 2012.

Today I made ~450 requests with an app key (no oauth token) and suddenly got a 502 response:

throttle_violation : too many requests from this IP, more requests available in 86281 seconds"

Did I do something wrong? The same API key used to work some weeks ago and I made several thousand requests per day without getting any errors.