What is a activator disk?
Basically the current ixtreme firmware isn't coded to run wave 4 games. The ixtreme firmware checks to make sure the video partition matches known data, this is to stop you getting banned when playing backups. ixtreme firmware will only play wave 3 games straight off the disk.
They introduced an activate.iso file that you can burn to a disk to override the video partition check as they predicted that microsoft would be releasing wave 4 sooner or later.
ixtreme 1.51 works with any game regardless of whether the video partition is intact.