Application File Not Valid in XBAP
When you see this error in XBAP application, which means you changed application manifest file from outside. To resolve this
we can use .net tool, which comes with .net SDK, called mage.exe or mageui.exe. More about mage.exe
Frequently used commands to resolve this is mage.exe -u and mage.exe -cc.
Actually this really happened to me, for one user, problem was remain even use mage.exe until he re-install .net runtime.