You probably realize that every save game on your XBox 360 matches up with one and only one gamer profile. So if you have a save game for Lisa, you cannot play it with the account named Bob. So why not just change names? It's not so easy.
We have an Xbox 360 base unit and had also purchased an Xbox 360 Elite with the larger hard drive. We then went about the complicated maneuvers to get the profiles and save games moved around from one hard drive to the other. However, this left us with the problem of having two systems and multiple profiles.
Say for example that James had been playing all of his Halo 3 games on my main BELLAONLINE account, since that was the one with LIVE Gold access for online multiplay. That BELLAONLINE account was now on the black Xbox 360 Elite. However, James wanted to do his Halo 3 playing on the white base Xbox unit.
You can't copy profiles - only move them. So BELLAONLINE could only be on the Elite or on the base 360 - not both.
I tried creating a brand new BELLAONLINE account on the base 360 with the exact same spelling and uppercase / lowercase combination. No such luck. Even after turning the unit off and on again, it still said that the Halo 3 saved games were associated with an "unknown profile". So it doesn't just remember the spelling of the profile name as the association. It must remember some unique ID attached to that profile account.
I understand of course some of the reason behind this. They don't want BellaOnline to run a game up to 99% and then hand over a copy to James, and have James do 1 minute of work, hit 100% and get an achievement for that. That makes sense. If you could randomly copy games and profiles around, then everybody would have 100% of all achievements and they wouldn't really be achievements any more.
Luckily, James hadn't played up TOO far on the Halo 3 / BellaOnline live rankings, only to two-chevrons-plus-a-half-diamond level. He should be able to re-do that on his new Live account he makes to go with the white system.
On the other hand, Ace Combat 6 would not allow us to copy the files, only move them. And as mentioned, leaving them on the old, white box with the ownership tag of "BellaOnline" left them as having an "unknown profile" now that the BELLAONLINE account is on the Elite black box. So our only choices are to move those save files to the Elite system, meaning they must be played on the Elite system, or to start over from scratch on the white system.
It goes to show, again, that you really should make one gaming profile account per person, and make sure you log in as that person when you play the game! You never know when you'll end up with two systems.