we all knows that windowsPhone7 application could also run on windowsPhone8 because it compiles it using windowsPhone7 architecture but i have an application which i made for windowsPhone7 it is also running fine on windowsPhone8 but the problem occurs when i change the targetOS from the properties of solution in VS from windowsPhone7 to windowsPhone8 it starts throwing exception in app.xml

is there any guidelines to follow if we are going to convert our project from windowsPhone7 to windowsPhone8

Thanks in Advance for your suggestions