Can't delete iPhone as presence sensor

In the mobile app I clicked on my iPhone, then SmartApps. It said, “No Installed SmartApps”. So I went to “Edit Device”, then “Remove”, and I got this message: “An Unexpected Error Occurred”. I then tried it in the IDE and got, “Mobile Presence could not be deleted”. What am I missing here?

Its likely you are using it somehow. Are there any third party apps that use it?