Hi Manual. First of all, great to hear that you're enjoying your T2.
I've owned mine since the beginning of November, of which include performing for several hours at a time, and utilizing registrations the same way you describe. Only on one isolated occasion, did my keyboard display that same message as yours.
I too was perplexed by that message, but since that time (over a month and half ago now) this hasn't occured again.
Unfortunately, I don't remember if I had gotten that message before, or after, having installed the 60gb HD and 1gb RAM. If I get that message again, I'll be sure to take note of it and share my findings here.
I'm curious now if any other Tyros2 owners here have ever got the Tyros2 message display: "T2 Memory is full and needs to reset".
Scott