When you attempt to use the slsvcutil.exe command line tool to generate a proxy for Windows Phone, you get an error that looks like:

Error: An error occurred in the tool.

Error: Could not load file or assembly ‘C:\Program Files (x86)\Microsoft Silverlight\5.0.61118.0\System.Runtime.Serialization.dll’ or one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded.


This is caused if the developer has both the Windows Phone SDK 7.1 or 7.1.1 AND Siliverlight 5 installed on the developer computer. Silverlight 5 changes a registry key that slsvcutil relies on to determine which assemblies to load.


The fix is to explicitly use a config file to specify the supported runtime version. The developer should supply a config file alongside the actual slsvcutil.exe file in the Windows Phone 7.1 tools folder (e.g., C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v7.1\Tools). This config file should be named:


and should have the following contents:

<?xml version ="1.0"?>
<supportedRuntime version="v4.0"/>
<supportedRuntime version="v2.0.50727"/>

After ensuring a file with these contents with the name slsvcutil.exe.config are in the same directory as slsvcutil.exe, then invoking slsvcutil.exe should work properly.


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