I received the following error yesterday:
"Unable to start debugging on the web server. An authentication error occurred while communicating with the web server. Please see Help for assistance."
I tried a fair amount stuff (technical term) including items outlined on Ryan Farley's post regarding the message. What ended up working [for me] was posted by Boaz in the comments of Ryan's blog. Here is the link to the MSDN fix:
http://support.microsoft.com/?kbid=896861#fixitforme
Warning: If you go the "Fix it For Me" route, you'll need to reboot.
If the above fix doesn't work, take a look at this.