Deployment and/or registration failed with error: 0x80070020

When trying to deploy onto a touchscreen phone, I get an error:

Deployment and/or registration failed with error: 0x80070020.

How do I resolve this?

You still have a process running on your smartphone.

On your phone:

1. Tap the Start key.
2. Tap Settings.
3. Select the System tab at the bottom.
4. Select the Memory icon.
5. Select the Running Programs tab at the bottom of the screen.
6. Select a task and click Stop or click Stop All to stop all processes.