Testfor Player Skulls in inventory

Hi,

When i use the command:

/testfor @a {Inventory:[{id:minecraft:skull,Damage:3s,Slot:103b,tag:{SkullOwner:"PoweredByPowerYT"}}]}

to testfor a custom player skull in my inventory (Head slot) it says:
[13:27:31] PoweredByPowerYT did not match the required data structure
and I have the skull in my inventory

Please help!