OK, I have never done a MKIII OS upgrade from such an early version. I was always under the impression that you could go from any version to any version, without having to go through an intermediate version.

The other thing that I do not know is whether every version prior to V17 also requires the Key CD, or is the Key CD something only associated with a V18 upgrade.

Here's a thought... plntzas is currently on OS 3-1/21, which was distributed on the V16.2 distribution CD. Can he just go directly to a V28 disk, as long as he has the key CD as well. I know that many people with 3-1/31 (V17.1 CD) upgraded directly to 3-1/63 (V28 CD) without loading the V18 disk first. They just needed the Key CD for that upgrade.

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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