Problem Reading Back-ups. Help me determine the cause.

Hey guys. Thanks for this wonderful forum!

Here's my problem. About three days ago I got my 360 modded. First day I played two different "back-ups". I switched back and forth between the games and had no problems whatsoever. I think I played for about 7 hours that day. Everything ran smoothly. Next morning I tried to turn on one of those disks, and got a "Unreadable disk. Please wipe with soft cloth" error. So I restarted the system, and the game started working. After about 30 minutes, it gave me the same thing. So I restarted again, but this time the game wouldn't even load. The screen would go straight to "Unreadable disk". I decided to turn it off for a while, and after a few hours turned it back on. It worked for awhile again, and then same thing. It almost feels like as if the system gets "tired" after playing a back-up and stops working until you turn it off for some time. What's interesting is that the disk doesnt give the Unreadable Disk error in the same spot. Sometimes its in the menu, sometimes in the random spot in the game. Its never the same. Im assuming the ISO is good because before burning I did a CRC check with xdvdmulleter and it said ISO is all good. Plus, the game worked like a charm the first day. My specs:

My system is about a year old (was sent by Microsoft when I sent in my broken one a year ago)
Hitachi drive (determined it by using this web-site
Using Verbatim DVD+R DL made in Singapore.
Burn using CloneCd with 2-4x speed.

P.S. Original games seem to work fine.
P.P.S. Could it be the lazer starting to go weaker and not being able to handle burnt disks?

Thanks in advance for any help!
Ugeous.