The LED code translates to a 59h. As you've indicated it's not in the diagnostic LED list. At this point we need to make sure you're using the right processor for your board revision. You can check that on the S1200BT Tested Processor List. Read the Notes at the bottom of the page.
Also verify the memory you're using is correct for the processor. See the Memory Subsystem section of the Technical Product Specification for more information.
If everything there is correct, troubleshoot by removing the memory and see if you get the three beep "no memory" installed indicator. And then reducing the system to a minimum configuration to see if you can determine what (if not the board) may be causing the issue.