Hi. It looks like firmware 3.21 is shipped with ROS 6.24 (on ccr) but I don't see this reflected in the changelog: http://wiki.mikrotik.com/wiki/RouterBOOT_changelog

What's new in 3.21:

*) disable RouterBOOT downgrade below backup booter version;
*) ar7240: fix wifi on Metal-2SHPn;

*) disable RouterBOOT downgrade below backup booter version;

I'm curious why you decided to do this. Since the backup booter always works and cannot be overwritten, you can't "brick" a RouterBOARD by downgrading the primary booter too far, and some people who know what they are doing might have good cause to do this (I personally can't think of any reason that I would need to do this today, but for example, those who are trying to use OpenWRT on newer batches of RB951U/G apparently have needed to do this, and it has worked for them, even though there is obviously no guarantee that running an older booter on newer board will work on account of subtle hardware changes and component sourcing differences).

*) ar7240: fix wifi on Metal-2SHPn;

I thought the Metal wifi problems were fixed in booter 3.19?

-- Nathan

*) disable RouterBOOT downgrade below backup booter version;

It is extremely strange decision! I ask you to cancel it, it is not very convenient!