If you get the error “specified communication resource (port) is already in use by another application.”
Browse to the folder: %LocalAppData%\Microsoft\Phone Tools\CoreCon and delete its contents.
Restart Visual Studio. Try and redeploy the app.
The Emulator runs within a virtual machine. Sometimes you might have to do hardcore things to get the emulator working again.
At the command prompt type: sc query vmm. This should return running if the VMM service that hosts the emulator is running.
To restart the service: first type sc stop vmm and then type sc start vmm.
Now restart the emulator.