在将目标框架从v4.0更改为v3.5后，无法找到名称空间。

I have 2 projects in a solution, 1 a dll, the other an exe. Both were using .net version 4.0 however no 4.0 specific libraries were used so it should be possible for me to safely change them to 3.5I have 2 projects in a solution, 1 a dll, the o