错误详细信息：
Unable to read the project file 'client.csproj'. Could not load file or assembly 'Microsoft.Build.Engine, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. 系统找不到指定的文件。
今天打开之前一个vs的项目，报出上面的错误，这个啥啊，昨天还是好好的，可以正常的打开的啊
于是，百度了一下：
搜到了这边文章：/s/blog_4696f46b01009mgd.html
里面提到：
RE:
Based on my experience, probably the NET Framework 2.0 is corrupt and the corrupt file/files remain after you reinstall . Hence, please try to uninstall .NET Framework 2.0 and then install .NET Framework 2.0 again.
You can download the “Cleanup_tool” from Aaron's blog to automatically remove the Framework.
Automated cleanup tool to remove the .NET Framework 1.0, 1.1, 2.0, 3.0 and 3.5/astebner/archive//05/30/611355.aspx
Alternately, you can manually do cleanup steps by following another article.
How to manually cleanup a failed .NET Framework 2.0 install
/astebner/archive//04/16/408856.aspx
我回头一想，想起昨天在捯饬WCF，对于这个NET 3.5.1给取消了啊
于是，我有勾选上了，再次打开解决方案ok！
不需要重启，勾选上即可！
