I had a problem yesterday with Visual Studio .NET. I was attempting to debug a .NET web application hosted on a non-default local website using host headers. Every time I tried to run the project I got a message saying that the current user was not a member of the 'Debugger Users' group. Suffice to say that, of course, the current log-on account was a member of this group. At one point I went as far as adding every available local and domain account to the group in a vain attempt to try to work out whay I was getting the message - nothing helped.
Eventually, by trial and error , a colleague and I worked out that we needed to add the site to the 'trusted sites' zone and the lower the security settings for trusted sites using IE options. I don't know why this worked, or why I got the message I did from Visual Studio, and unfortunately I don't have time at present to dig deeper.