sounds like a bad cd-rom drive to me. i did an install for an office network rollout and they had a bunch of old acer p4's with oem cd-rom drives. every time textmode hit a bigger file they'd just be like, nope, sorry, can't give you that, we're garbage. we ended up having to go around the office swapping out cdroms. in every case the drive we swapped in was older than the drive originally in the computer. ridiculous.