I am sorry to hear that you were unable to watch Sky Sports as the device was giving an error of unregistered.
When you sign into your account, on the right under My Profile there will be Device Settings and Sky Movies & Sky Sports. Device settings will show devices that are registered to use TV Anywhere and Sky Movies & Sky Sports will show devices registered to use Sky apps. Is the device that you mentioned registered under Sky Movies & Sky Sports. If it is not you can remove one of the devices that are not in use and replace it will the device in question as you have a change available.