C # Add DLL reference after adding a namespace error solution

Cause: The target frame of the class library DLL is inconsistent with the target frame of the project, right-click the Project project--〉 property---the "target frame" target framewiork under the 〉application tab, and the class library that is encountered is:. NET Framework 4 while the actual project framework is the. NET Framework 4 Client profile, it is possible to change the project target framework to match the class library, for example, this approach solves most of the problems similar to

C # Add DLL reference after adding a namespace error solution