I hate that, and it seems that every time I (or a co-worker) gets the error “Unable to Start Debugging on the Web Server” on a machine when attempting to debug an ASP.NET project, I have to scramble to remember what to look at. Here's a few things that has worked for me to get things working so you can debug your ASP.NET project when/if you ever get this error:
- Make sure that IIS is configured to use Integrated Windows Authentication. Look for the checkbox on the Authentication Method dialog launched from the Directory Security tab of the site properties.
- Make sure that HTTP Keep Alives are enabled. You'll find that checkbox on the Web Site tab of the properties dialog, in the connections section.
- This one is strange, but it seemed to do the trick for many out there, add http://localhost to the trusted sites in Internet Explorer. To tell the truth, this seems to be a fix for the symtoms, not actually fixing the problem itself, but if it works it works. BTW, you'll have to uncheck the “Require server verification (https:) for all sites in this zone“ checkbox to add it as a trusted site.