That is the original version of the OS for the MkIV. The MK4 units were shipped with 4-1/10 from the factory at the start (from 09/02 to 10/02) but this version had some known bugs and therefore BMW put the text "T20.10" as a dealer reminder to upgrade with the V20.1 CD when available. You likely see "T20.10" when the unit is first started up.
Definately get that thing upgraded. My advise is to find an interim release to go to before taking it to V26.
See
http://www.xoutpost.com/showarticle-59.html
Jeff