I had a Problem with certain DVDs not reading very well in my DVD ROM and they did read fine in my DVD Writer, this has only happened a few times out of 50 or so,
the error I got was, Data error (cyclic redundancy check) and happens about 50% the way through the disc,
by accident (cough by sheer will, determination and lots of skill) I have found out why,
when I had this problem it was just before I added a Raid card to expand the number of hard drives I can support, and after adding the card this problem went away,
I have now tracked it down via 'trial and error' to 1 thing, if I select Slave as my DVD ROM configuration (I have 2 DVD readers which is another reason I wanted more IDE channels) the slave gives this error, the one selected as Master doesn't, if I swap the Master / Slave Jumper setting over then the former Master (now slave) gives this error, and the former Slave (now Master) doesn't,
this is probably why most people tell you to use your burner to read when you have problems, as this is generally set as Master,
I just thought it might help someone else sometime.