I suspect that you have a bad laser. There is probably a reason that the previous owner had the CD map instead of the DVD map when you bought the car-- the car would have originally come with the DVD-based map disk.

Your OS version confirms that it is a MKIV. Plus, the fact that you updated it to 4-1/00 further confirms it is generally functioning well and has the OS updates it needs to read the newer dual-layer DVDs.

I am not aware of any hardware differences from the earliest to the latest MKIV nav computers. (There may be some, but they are probably not significant.)

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SOLD
2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input