I have gotten this before...Did you change any code while the project was running?  You debug information got screwed up when you changed the code

The way I got rid of it (but this didn't work for my co-worker).  Try deleting the website the DNN instance is attached to and/or deleted the application pool it is running on.

Are you running the source code? or the starter kit?  If you are running the starter kit, delete the solution file that VS created for you when you created the site.  should be named something like "localhost.sln" or whatever you named your site.

Try those things and it should come back...if those don't work, you might wanna check online for another solution...but what I described above is what I found and seemed to work for me.

Hope that helps.

Thanks for the help. I did as you suggested and it did fix it. I found a lot of suggestions out there on the web and tried many of them.

What ended up working for me was right-clicking on my solution in the explorer, opening the Property Pages, selecting Start Options, and then under "Server" changing it to "Use custom server" and specifying http://localhost/virtual directory name.

I certainly learned that it is a BAD idea to change your source will running your application. At least I believe that is what caused my problem.