Error 4 The type or namespace name '' could not be found (are you missing a using directive or an assembly reference?)
You may get above error mainly in following circumstances:1.
You have not referenced the .dll whose class you are using into your project. So right click the project and select Add Reference ... now select the .dll by clicking on Browse button from left panel of the dialogue and Browser button at the bottom.2.
Even if you have referenced the correct .dll into your project but if the .dll framework version mistmatch is there, you will get this error. eg. Your project is in .NET 4 and your .dll is build in .NET 4.5. So you need to make sure that same version built .dll you are referring.
Hope this helps.