reading / copying multisession data DVDs

running win xp using nero 6 (or so I beleive) and lite-on dvd writer I burnt
4.7 gig (single) dvd+r disks, to back up cca 50 gigs of mp3 music (my external 300 gig drive died once, leaving me with a bill to foot for recovery) in multisession format
most of the dvds are all right, can ship them back to the external drive
however the ones containing larger files (2.5 gig) will take a long time to read
and will end with a message that sounds like "redundant cycling error"????
is there a way of recovering those files and transferring them to my external drive?
I am mad about my music, would appreciate a solution
thanx
dead vulture