What I don’t understand from your post is whether you just took the two cubes out of the box(es) and attempted connecting them or if you configured them (via Winbox or Webfig or SSH).
In the first case it could be a factory mis-configuration of one device, in the second it could be a mis-configuration you made.
Or it could be a DOA device, but let’s start checking that there are no issues with current configurations.
Follow this post:
http://forum.mikrotik.com/t/forum-rules/173010/1
and attach to your next post the two configurations of the two devices, so that they can be reviewed.
OR check your configurations against these two known default ones:
http://forum.mikrotik.com/t/wireless-wire-cube-preconfigured-plug-n-play-doesnt/173973/1
Do review the whole topic:
http://forum.mikrotik.com/t/wireless-wire-cube-preconfigured-plug-n-play-doesnt/173973/1
it seems like it was originated similarly.