C# 2008 project file 转换为 C#2005 project file.

1.将.Sln 文件中的10.0改为9.00. 2008 改为 2005

Microsoft Visual Studio Solution File, Format Version 9.00

2.在.csproj文件中增加<Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />