It seems that changing from a Core (oem digitial entitlement) install to a generic Pro key doesn't work. I've tried both via slmgr and settings - activation - change product key. Any ideas? Errors received: 0xc004F069 (slmgr) and 0x803fa067 (settings-activation-change product key)
In my tests i had it happen on newer Windows versions that the process failed when being online. It offers to start the process and fails shortly after. Try process offline . EDIT: slmgr error reports SKU not found. What key was used?