This is a warning because we just went through searching for the error for some weeks.
In many cases the managed systems (respectively their service processors) reside on their own network, together with the HMC(s) managing them. In this setup usually the HMC acts as DHCP server for the service processors.
In our environment, though, this was not the case. We used our central DHCP server to give out IP addresses to the service processors. This worked - initially. After some time we started to experience duplicate IP addresses in the net and these were the ones given to the service processors, which in turn made the managed systems unavailable for the HMC.
We found out the following: the service processors are indeed DHCP-clients of sorts, but they do not fully adhere to the standards. In particular they do not renew their lease once it expires but simply pretend that the IP is theirs forever. The HMCs DHCP server process seems to know that and does not give out the IP address again even though - in terms of "real" DHCP - the address is not taken any more. Our standard DHCP-server, alas, did not know this and gave out the addresses to other systems. This was why we found duplicate IP adresses in the net. The service processors simply hadn't bothered to renew their IP leases and subsequently the DHCP server has reassigned them to other hosts.
Solution was to switch back to the HMC as DHCP server for managed systems with its own reserved address range and rediscovering the MSes on the HMC.
I hope this helps.
bakunin