While working on the same machine, I often log in under two different user accounts - one for work and another one for testing with full (Administrator) privileges. This generally doesn't cause any problems, and in the context of the classic Windows application model, should not be causing any issues at all. With Metro in the game, however, the situation changed a bit.
Let's say you have this scenario - you work with Visual Studio 2012 RC, and you have one Metro app solution, created under User A. You then log out, and open the same solution, located in the User A document space, but this time as User B. Given there are no policy restrictions, you are able to work on it, but when you try to debug it, you might see this:
Although you are not directly impersonating the creator of the solution, you are trying to install it based on the user settings. To solve this issue, all you have to do is give the application a new ID. Open Package.appxmanifest and change the package name:
It doesn't have to be a GUID, as long as you can ensure the fact that the name is unique. After that, build and deploy. The package should become available in the Metro start screen and you will be able to launch the application.