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