Recently I started seeing this error on our internal TFS SharePoint sites. These sites use the Excel Dashboards and if I opened more than a few sites at a time, I would start getting the following popup error:
Unexpected callback response!
Error: 400 Bad Request
Bad Request - Request Too Long
HTTP Error 400. The size of the request headers is too long.
It didn’t seem to matter which browser I used or whether I ran in Private Mode (to get a clean session each time) – the result was always the same error.
Save this as a .reg file and run it.
Windows Registry Editor Version 5.00
After setting the settings, you will need to restart your server so that HTTP.sys can pickup the new parameters.