The universe type cannot parse the assembly system. Design, version = 2.0.0.0

When I place an externally referenced control from the toolbox, I am prompted: The universe type cannot be parsed.ProgramSet: system. design, version = 2.0.0.0, culture = neutral, publickeytoken = b03f5f7f11d50a3a. After searching online for half a day, I finally found a solution, this problem occurs because I chose the framework when creating a new project. net4.0, however. net4.0 contains two types during installation, as if the default is. net4.0 client profile. When added below, the above error will be reported. The solution is:

Right-click the project in Solution Explorer, select properties, and change the Framework version of the framework to. net4.