The Windows Phone Developer Tools 7.1 allows you to create and develop applications and games that target both Windows Phone OS 7.0 and Windows Phone OS 7.1. The Visual Studio project file for an application or game can only target one version of the Windows Phone OS. You can upgrade a project that targets 7.0 to target 7.1 in the Visual Studio UI, but once you upgrade, you cannot downgrade it from the Visual Studio UI. Because of that, the upgrade UI recommends making a backup of your 7.0 project before proceeding with the upgrade process.
If you have an XNA Game Studio Windows Phone 7.0 game project that you have upgraded to 7.1 and you didn’t make a backup copy before the upgrade, you can use the following steps to manually downgrade it to 7.0:
- Make sure that your project and solution are not open in Visual Studio
- Open the project file (*.csproj or *.vbproj) in a text editor such as Notepad
- Locate the following property value:
- Remove the property value entirely or set the value to 0
- Re-open the project in Visual Studio