I've got a brand new T5220 with four 2GB FB-DIMMs in it. Initially it had eight 2GB FB-DIMMs in it, but they weren't all the same part number and ILOM would report that the box was working in a degraded memory condition. It would not even allow an OS to be installed. Sun documentation states that all FB-DIMMS in a branch must have the same identical part number, although I am not certain what a 'branch' refers to in this server.
So, I removed the second set of different FB-DIMMs that had been added after the box was purchased. This left the original four 2GB FB-DIMMs with identical part numbers (M395T5663QZ4 by Samsung).
The above change removed the error message about the box working in a degraded memory condition. And, from the ILOM prompt, /SYS/MB/CMP0/MCU0 says it is enabled. In fact, everything shows enabled. But, when the box is powered on, just before you get the OK prompt, there is a message from the OBP that says that /SYS/MB/CMP0/MCU0 is disabled. At this point you can go back into the ILOM and you will see that MCU0 still says enabled.
Why are these reporting oppositely? It isn't as thought I can go into the ILOM and mark MCU0 as enabled--it already IS enabled. There is a SUN patch for the firmware that talks about this problem (136932-10) but the version of OBP that the patch brings the OBP to is lower than the OBP is right now.
If you answer, keep in mind that there is no OS installed on the box, yet.