As soon as Automap 4.1 was released I tried it with my Nocturn keyboard and REAPER 4. After extensive troubleshooting I was unable to get HUI mode working with it, other functions work though.
After emailing with their tech support I started a thread on the forum about it. It seems I’m not alone with this issue, it is affecting both mac and pc users. Unfortunately Novation can’t give us a fix for a while.
For the time being stick with version 3.4.7
[update Feb 21 2012] The latest Beta of Automap adds REAPER HUI support. Read more here.