Konstantin,
I see your action is pointing to "Current Screen:>Current Object" Is this the object you are tried to change?
Also, is it a MeanObj?
If both are yes, then on your transaction step, you shouldn't need to set a target object. This is because it will default to the object of the action, which is current set to the "MeanObj" current object.
The point of the Target Object is if you have an action updating one transaction, then you within the same action, you need to target and update a different object.