You can directly upgrade from v21.2 (4-1/12 = 21.2) to v29. The only issue which could happen (please someone confirm this) is when you upgrade from <v17, where the system will ask you for a "key cd". This CD is available for download somewhere in the forum.

I've sucessfully updated a friend's E46 from v24 (4-1/40) to v28 (4-1/80).

(PS: how does the version show for <v17 version? 4-1/??)

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