RobotStudio event

RobotStudio SDK

while compilation this command: Station station = Station.ActiveStation;  makes this error  this error : System.TypeInitializationException
  HResult=0x80131534
  Message=The type initializer for 'ABB.Robotics.RobotStudio.Stations.Station' threw an exception.

Inner Exception 1:
ReflectionTypeLoadException: Unable to load one or more of the requested types.
Could not load file or assembly 'System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. The system cannot find the file specified.
Could not load file or assembly 'System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. The system cannot find the file specified.
This means that the connection with RobotStudio through SDK was not established. What is the solution for that?
I appreciate any help!