Failed to subscribe on signal ".../Target/Tool Changed" / "../Workobject Changed"

in RobotStudio
Hello, i'm trying to program my first robot (YuMi) and got some issues right at the beginning.
For testing, i just defined a few targets and added smart-gripper.
When i try to run the simulation, an error says : "Failed to subsribe to signal: "IRB14000\Mechanical Units\ROB_x\Target\Tool Changed" and "...\Workobject Changed" for the left&right arm.
I think this is an basic issue, but i cant figure out what to do.
Another problem: i cant use the "g_xxx" identifier for the smart grippers, even i imported the library and installed the addin.
Thanks in advance
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Comments
Is the error because you are you using signal analyzer?
Are you running the program from the RAPID tab or as a simulation?