This is the original default roster for NBA Live 99, containing final 1998 season rosters and none of the Class of 1998 rookies. Normally, it's overwritten by the official patches for NBA Live 99 and cannot be reloaded, unless the files are copied over from the CD-ROM.
Please note that the official patches, including updated 1999 season rosters, can be found here. It's recommended that you install them, and then use these rosters if you wanted to play with the original defaults.