NBA2k11 Roster Update... How to convert .ROS files to .iff?

I downloaded the game but its roster file is "roster.iff", all the roster update patches tht I download are "roster.ROS", if I manually change the extension, the game won't work, does anybody know where can i download a .iff roster file, or how to convert .ros files into .iff? Thank you 4 your support. Go Lakers!