this is nginx 0.6.34. We run some fairly high volume facebook sites and have had problems with 400 errors now for months. It only happens on one part of our site that runs inside an iframe. At first I thought it was cookies that were too large. I increased some of the buffers but that didn't appear to make any difference. A couple of days ago we took out all the code that was generating large cookies, and are still getting 400 errors. The really frustrating part is that nginx refuses to log the error, so we can't even debug it properly.

This is with nginx as a reverse proxy for rails.

Chris