There shouldn't be a need to have the RMM4 installed, regardless of the system, to update the BMC portion of the update package. Please make sure that your system meets the requirements for the update. If possible try an earlier version of the firmware to compare results.
You may also use the http://www.intel.com/support/motherboards/server/s2600cp/sb/CS-033738.htm BMC Force Update jumper . For this, you need to move the jumper from position 1-2 into position 2-3 during the update. Once the update is completed, please move it back to its original position.