I’ve solved it out 
On this forum I read an topic with a similar problem.
I did the follow steps and my thumbnails where changed to the right one :)thing to completely
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Turn off the WD using power off on the remote.
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From the computer find “thumb” in directory from the .wd_tv directory in the root HUB directory. Then, delete the whole thumb directory, or navigate more surgically to find the directory you changed or even the actual thumb files. The WD regenerates them rapidly, so it’s not a hassle for me with several hundred thumbs to delete a whole directory.
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Restart the WD using power on from the remote,
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Then immediately do a “device restart” from within the menu. (Home → Setup → System → Device Restart). This is more like a reboot than just powering off/on with the remote.
Thanks for the help.
