I'm not entirely sure what caused it, but after backing up the source for the site and reinstalling Windows, when I went to load my backed up site, the project failed to load, and simply said "System.Runtime.InteropServices.COMException".  There we no errors before backing up, and the backup was simply a copy/paste with no compression, so there was a slim chance of corruption.  Visual Studio still loads, and lists the project, but it's inactive.  Right clicking the project name(not the solution), and clicking "Edit xxx", where xxx is your project name, brings up the XML for the project file.  Doing some digging around in there led me to the "ProjectExtensions" element at the bottom, and in particular the "UseIIS" node.  After setting it to "False" and reloading the project I was back to work.  But the root cause was because I had forgotten to reinstall IIS after my reformat.  Note that just deleting the whole element, works too, but the section is regenerated after the project is reloaded, and sets "UseIIS" to false.