A reference to a higher version or incompatible assembly cannot be added to the project - Windows Phone

Problem : Got following error while adding reference(dll) to Windows phone project.

Microsoft Visual Studio Express 2012 for Windows Phone

A reference to a higher version or incompatible assembly cannot be added to the project

A reference to a higher version or incompatible assembly cannot be added to the project

Solution:

Go to the folder where that dll is stored.
Right click on dll file -> Properties
Then click Unblock

A reference to a higher version or incompatible assembly cannot be added to the project