Just to clarify for anyone reading this that might get the wrong idea: Nexus Ultimate does not 'expire', this is NOT rental nor subscription software.
What DOES expire is the 1 year period of free updates. After that year, if you want to get more updates you need to renew the update subscription for another year for a fraction of the price you originally paid for the application. You DO NOT have to do this unless there are updates you want which are already outside your update subscription period - also, there are NO penalties for not renewing 'on time'.
When you DO renew, you get another license key file, which you must install as you did the first one, so it replaces the old license key file. I guess this is what gevansmd wasn't realizing at the time, he was probably trying to apply the old key file instead of the new.