Beware, long post...
I've been dealing with this darn "Error Reading DVD" issue on my wife's 06 Commander for waaaaay too long. I was pretty close to removing it and sending it to a place that claims that it's a common issue and they can fix it for a low, low price of just $275.
I started searching online for fixes and couldn't find anything (months ago). I pulled the unit out before our family roadtrip from Chicago to Sarasota this summer and removed the OEM fan on the back because I didn't hear it running anymore and figured that coulda been the problem (overheating). I wired up a small fan from the local scientific supply house and it seemed to help out. The Error only came up every few days or so. Then just as we were entering Florida after a day-and-a-half of driving the Error came on and didn't go away. It's been busted for a couple months now and I've been dreading the fact that it's gonna be $275 for a fix.
When I researched causes, the reasons for the error varied: overheating head units, bad copies of a nav disk, dirty disks or dirty lenses. Since I fixed the fan issue and tried with a brand new burned disk, I figured it was the lens. I googled how to disassemble a REC NAV today figuring I'd give it another shot and found this
I kept disassembling until I finally got down to the Nav DVD player, gently cleaned the laser lens with a q-tip dipped in isoprophyl alcohol, reassembled the entire mess and reinstalled the unit into the Jeep. Start to finish was 60 minutes.
I said a little prayer (something like "Dear God, if this works, I'll never swear again"), turned it on and it worked like a champ! Now I gotta stop swearing.