Check out this KB Article.
>I am receiving the a debugging error "Error while trying
>to run project: Unable to start debugging on the web
>server. Access is denied. Would you like to disable
>attempts to debug ASP.NET pages for this project?"
>after installing windows 2000 professional, .net was
>working quite fine with windows 2000 advance server. I
>have tried different options such as adding debug group,
>changing the configuration of IIS to debug and
>IIS but it is still creating problem.
>Any one can help me..