RobotStudio event

How can I write to Rapid Data by using PC SDK ?

Hello all

I'm trying to write to Rapid Data (RobTarget) by using PC SDK.
I'm using 'Value' property and 'FillFromString()' method as in the code below.
However, if I do this, I will get this error:
C0048409 : An argument specified by the client is not valid for this type of operation.

RapidData rd = controller.Rapid.GetRapidData("T_ROB_R", "Module1", "Home");
IRapidData data = (RobTarget)rd.Value;

using (Mastership m = Mastership.Request(controller.Rapid))
        rd.Value = data;   

I'm just a beginner of PC SDK that I might make mistakes in this code.
Would you tell me where I'm wrong?

Best regards,