Quote Originally Posted by diamond1 View Post
Well, so I can not use DPU anymore, or will it penalize me?
a 400 error as identified in RFC 2616 is identified as:
10.4.1 400 Bad Request

The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.
I would say that response is appropriate for the information needed in order to provide an appropriate response. The Official Google Webmaster Blog discusses 404 errors, which this condition is not really the issue as the "page" exists, but nothing can be done by going to just that page, being authorized does not help. And from the other side, the server isn't exactly having a problem, but it doesn't know or can't process what was provided. On a "day-to-day" operation, this has no effect, but on someone trying to develop something, it can be discouraging if 400 is the response. :)

Basically, there should be no reason to stop using software that uses ajax style calls and identifies that crawlers shouldn't be concerned with the returned content. That is unless there is something specific being returned that is intended to be the content indexed... That is a different story and would have to be handled differently.