The subject error just pops up for a project that has been running fine for a long time. It comes from IIS Express when running a Web application in Visual Studio. I’m not sure what causes it, but it might have been a side-effect of debugging other errors with Hyper-V and VPN. Looking around, the advice for fixing this was sparse and/or the typical VS repair/rebuild recommendation. Figuring out how to run as Administrator isn’t a valid solution either because it’s less secure and these days I can do a lot of work in VS without being administrator, like I was doing in this project. I did find one blog post, by Mark Hugh Neri, that was a good solution:
Workaround for URL binding failure error in IISExpress
The only thing I did different is that in VS you can right click the project, select Unload Project, and then right click again and select Edit ProjectName.csproj. After that, you can right click the project and select Reload Project to start working again. Removing the DevelopmentServerPort and IISUrl tags causes VS to re-generate a port number and the project works well after that. Another thing I did was to open my Documents\IISExpress\Config\applicationHost.config file and delete the old sites, but I’m not sure it was necessary.