We recently upgraded from EPM 2007 to EPM 2010 and found something similar. I’m not sure if it is the same issue, but from time to time, when we open existing (migrated) projects, the team members do not appear on the right side of the screen in the ‘Build Team from Enterprise’ menu option. This is fixed by cancelling out of that screen and then saving the project. You then go back to that screen and the resources reappear again.
