手动安装吧，将Silverlight 4 Tools for Visual Studio 2010.exe改成rar文件，解压缩，按照下面的步骤安装：
1.silverlight_developer.exe
2.Silverlight_UninstallKB976272.exe
3.silverlight_sdk.msi
4.VS10-KB982218-v4.exe
5.SilverlightTools_Package.msi
6.Silverlight_UninstallRIAPreview.exe
7.RiaServices.msi
8.Silverlight_UninstallFSharpRuntime.exe
9.FSharpRuntimeSL4.msi
手动安装Silverlight 4 Tools for Visual Studio 2010
原文：http://www.cnblogs.com/CandiceW/p/4227457.html