I managed to restore a 250gb image which can be found in the wd community forum. The device works fine with the firmware version 03.04.01-219 which is included in the image.
When i want to update to the latest version, the device seems to finish the update without an issue and the shares are still accessible, but the UI is not working. I already tried other brothers and resetting the cache, but that doesn't help at all.
Can someone tell me what i could try to resolve this issue?