transferring files over lan...losing quality?

I have a simple 2 pc lan setup with capable machines on each end. I often
rip dvd stuff for later editing. Every now and then, I may want to transfer
the files over to the other machine. I can use the files on the machine it
was ripped on. However, If I copy the file as a whole, it is sometimes
unable to be used for editing on the other machine. This goes both ways
with each pc. I dont try to hog the network with downloading, firewalls,
other transfers etc... In other words, that is all the two machines are
doing at that given moment, exchanging a large 4 gig file.

This problem only seems to happen in about 1-outta-10 times. No ryme or
reason I can particularly think of. Both machines run XP Pro. No other
network problems have ever surfaced, just this type of transferring.

I have tried other related NG's, but have not gotten far with the responses.
I figure you guys might know of some sort of XP or network limitations to my
dilema.

Thanks all,
SL