'03 DVD-based Nav doesn't recognize Map v.6.5 disk anymore!! Help!

Hi, I updated the firmware a while ago when I got the car last year, and I ordered the Map disc version 6.5, and it had been working fine since then UNTIL yesterday, when I played a DVD using the "trick" to make it playable while driving (which I have done many times w/ no problems/affects) and it seemed like everything was fine, but then when I reinserted the MAP DVD disc, it did not recognize the disc anymore and it rejected it after about a minute. So I tried putting the old 6.0 disc in there and it recognized it and worked fine. So I tried to update the firmware again using the same update CD, but it didn't recognize the CD (which means it's up to date and no update required, as it said on the instructions). Anyone has came across this problem?
My car is an '03 CTS and I got the Nav replaced by the dealer early this year. I would appreciate any inputs