System.UnauthorizedAccessException when deploying to Windows Phone 8

I am almost head-desking over this problem. Here's the deal: I'm trying to build stuff for my Windows Phone 8. I downloaded the SDK, make a small Unity project with just a GUIText and deployed it. Magically, it worked! So awesome! So I decided to add a sphere that moves. Built, deployed, boom! Worked again! I then tried to add back-button support with code like so (in C#, btw):

 bool backPressed = false;

 void Update()
 {
     if(Input.GetKeyDown(KeyCode.Escape))
     {
         if(backPressed)
         {
             Application.Quit();
         }
         else
         {
             guiText.text = "You pressed the back button! Press again to exit game."; 
             backPressed = true;
         }
     }
 }

I went to deploy, and I got this error:

 { a bunch of stuff with serial numbers and whatnot that I'm not going to put on the internet }
 [13:54:14.233] Deleting app icon.
 [13:54:14.264] System.UnauthorizedAccessException: Access is denied.

    at Microsoft.VisualStudio.DeviceConnectivity.Interop.ConManServerClass.InstallApplication(String in_pProductId, String in_pInstanceId, String in_bstrApplicationGenre, String in_bstrAppIconPath, String in_bstrXapPath)
    at Microsoft.SmartDevice.Connectivity.Device.InstallApplication(Guid productId, Guid instanceId, String applicationGenre, String iconPath, String xapPackage)
    at Microsoft.SmartDevice.Connectivity.Wrapper.DeviceObject.InstallApplication(Guid productId, Guid instanceId, String applicationGenre, String iconPath, String xapPackage)
    at Unity.Program.Run(Guid appId, String iconPath, String xapPath, Boolean test)
    at Unity.Program.Run(String xapPath, Boolean test)
    at Unity.Program.Main(String[] args)
 [13:54:14.264] Exiting Windows Phone 8 Runner.

What the dang?! I tried a bunch of stuff to fix it, starting with just trying again - that didn't work. I commented out the code I just added - nope. I deleted the generated VS2012 solution and rebuilt it - that didn't work either. I unregistered and then reregistered my phone, but to no avail. I disconnected and reconnected my phone. I closed and reopened Unity. I even went so far as to unregister my phone, unplug it, shut down my computer, turn it back on (not using the 'Restart' action - literally 'Shut Down'ing) reconnect and reregister my phone, and restart Unity. Nothin'. Same dang error.

What's going on? How can I fix this strange problem?

Update:

Just built the app detailed here. It deploys fine, but the Unity app still does not.