Error Type:“The Web application at http://sharepointserver could not be found. Verify that you have typed the URL correctly. If the URL should be serving existing content, the system administrator may need to add a new request URL mapping to the intended application.”

 building applications in Visual Studio 2010 as Console applications or Windows Forms application,i got above error.

1. Under Project Properties –> Application, Ensure that the target framework to be compiled against is .NET Framework 3.5

 2. Under Project Properties –> Build, Ensure that the platform target is set to x64

Solved this error