Could not find type or namespace name "* * *" (is missing a using directive or assembly reference?) Error resolution

This error is due to the. NET version issue

Because of the current project. NET Framework is a. NET Framework 4client profile, and this client profile is a lite version of the. NET 4.0 framework, causing the referenced class library to be unusable .

Right-click the current project, select the Application tab on the left, and change the target frame to . NET Framework 4.

The official introduction is this:

. NET Framework 4 Client Profile provides a subset of the features in the. NET Framework 4. This client profile is designed to run the client application and enable the fastest deployment for Windows Presentation Foundation (WPF) and Windows Forms technology. Application developers who require features not included in this client profile should target the full. NET Framework 4 Rather than this client profile.

Could not find type or namespace name "* * *" (is missing a using directive or assembly reference?) Error resolution