Byrne Resse, Movable Type Product Manager @ Six Apart announced movable type v4.21 which is basically v4.2 with a two major bug fixes, one regarding custom fields data, and the other regarding the archive mappings.
In an effort to make your life easier if you want to upgrade a movable type installation from v4.2 to v4.21 I've created a patch which you could unzip and upload to your server
The patch is available both for Movable Type Professional and Movable Type Open Source and you could download it right here:
1) Movable Type Professional v4.21 (upgrade from v4.2)
2) Movable Type Open Source v4.21 (upgrade from v4.2)
If you find this patch useful and want to make a donation, you could do so via paypal to firstname.lastname@example.org
Also, if you need any movable type consultancy service, including installations, upgrades, recoveries or anything else, just get in touch via email or using the contact form above