You get intermittent http 400 error messages while accessing your website hosted on IIS server. There is not specific pattern in the failure.
In HTTPERR logs you see an entry similar to the following
2011-04-05 05:21:46 127.0.0.1 - 127.0.0.1 80 HTTP/1.1 POST /MyHomePage.aspx - 1 Timer_EntityBody DefaultAppPool
IIS Logs will simply show you a 400 0 64 entry.
User may experience varied behavior. Like they may see the actual http 400 error code or they may see a generic "Page cannot be displayed" error message after browser spinning for a while. This behavior is irrespective of the IIS version(6.0/7.0/7.5+) and website type(ASP/ASP.Net)
Reason and Resolution: In multiple instances I have found that this issue is occurring because of the AVG Antivirus. AVG has a feature called LinkScanner which for some reason causes this situation.
To get rid of this, you need to 'disable' LinkScanner feature of AVG. No reboot is needed.
There were instance when the website was running just fine and suddenly this issue popped-up. It was discovered that it is quire possible that an anti virus update has enabled LinkScanner feature which was disabled previously.
I see lots of unresolved posts for similar issues. Hope this will help.