Brocade: "There is no standby. Reason: u2: not operational"

I came upon this not long ago and found the following when doing a "show stack".
Core#sh stack
alone: standalone, D: dynamic config, S: static config
ID   Type         Role    Mac Address    Pri State   Comment
1  S ICX6610-48P  active  748e.f892.1234  0 local   Ready
2  S ICX6610-24P  member  748e.f8e7.4567   0 remote  NON-OP: image mismatch

    active
     +---+        +---+
 =2/1| 1 |2/6==2/1| 2 |2/6=
 |   +---+        +---+   |
 |                        |
 |------------------------|

Note: There is no standby. Reason: u2: not operational,
Current stack management MAC is 748e.f892.1234
Core#


Current stack management MAC is 748e.f892.1234
Core#Warning! put unit 2 MAC=748e.f8e7.4567 to non-operational, reason= config mismatch
Unit 1 loses all neighbors.
Active unit 1 deletes u2 but keeps its static config.

So the solution in this case was to make sure the images on both the ICXs were the same.  They were not, as you can see from the first highlighted portion of the message.  It shows the topology of the stack, but its non-operational.  Upgrading the image resolved the problem here.