Ended up being bad motherboard.  Dell replaced board this morning - resolved issue. 
Good afternoon,  I have a Dell Power Edge R710 Server that we recently ordered a ram upgrade kit.  All Dell original certified.  (18) - 16GB modules. 2CPUs.  When I load up all 18 DIMM slots and boot up, I receive the error message "membist failure - the following dimm has been disabled by bios" and the error points to DIMM slots A3, A6, A9 and notes that I now have 240GB memory (missing precisely the 3x16GB modules that have been disabled)  I've tried swapping those 3 modules with another 3 modules, still same message.  I've tried swapping all A modules with B modules and still receive the same error point to the same A3A6A9.   I've tried to take out CPU2 and all B modules, and run with 9x16GB modules and that was even worse.    Our main hardware guy is on vacation and I'm lost - anybody have any ideas?  Thanks, Mike
PE R710 - Unable to get full 288GB ram recognized. Membist error A3, A6, A9