No worries, MCB was part of CMS, but it hasn't been updated in that plugin. CMS will be phased out, since MCB is the only feature that's still useful. WordPress and/or plugins have supplied other and better alternatives to the other features.
Multiple content blocks will be updated more frequently, it's actually just rewritten since it was slowly breaking a little more each WP update. It was a matter of time before it stopped working.
The new update migrates data from the old version (or the CMS plugin) to data that can be used by the newest version, so you don't have to worry about losing any of your data (but back-up when updating, just in case!).
Also, we will deploy some new plugins in the near future that we will keep supporting.