From the infocenter :-
Cause: The command (Initiate Self Load) sent to the IOP telling it to locate the selected load source device and load or reset itself has failed. The IPL will attempt to continue, and depending on the type of failure, the load source device may be retried or skipped.
Recovery: Look for SRCs in the PAL relating to the device location specified in words 3-6. Follow the recovery actions for problems found. Then, retry the secondary partition IPL. If it continues to fail, contact your service provider.
Problem analysis procedure: The values for words 3-6 are as follows:
Word 3: Bus address information
Word 4: Board address information
Word 5: Card address information
Word 6: Unit address information
These values can help you to identify the hardware that caused the error.
<a href=”http://publib.boulder.ibm.com/infocenter/systems/scope/i5os/index.jsp?topic=/rzahb/rzahbsrclist.htm&tocNode=toc:rzahg/i5os/18/4/1/”>SRC (System Reference Code) List</a>
So it looks like a hardware problem. Is there anything recently changed hardware-wise on the machine?