Debugging Windows Phone apps and error “A specified communication resource (port) is already in use by another application.”

Sometimes when you try to debug a Windows Phone app through emulator with Visual Studio, you may encounter the following error:

A specified communication resource (port) is already in use by another application

One possible reason for this is that Visual Studio tries to debug an app which isn’t deployedto the emulator.

For example, if you set the startup project like this:

And then through Visual Studio’s Configuration Manager you don’t check the “Deploy” for this particular project:

You will get the error when launching the debugger.