I Moved this to Mobile Security. As this is a holiday and the only place to get fast service would be online support.
I don't use Mobile Security but would assume you have to uninstall it from that device and then proceed to your online account and de-register that device there if not already done automatically.
Then you'd try again from scratch.
Other than that I can only suggest online chat with Support: http://service.mcafee.com/ProductSelect.aspx?lc=1033&sg=TS&pt=1