Have you tried removing the AC power plug from the system, waiting 60 seconds and then re-powering system?
It soulds like the BMC FW got corrupted somehow during the flash.
AC cycle will restart teh BMC.
If it still does not work, try removing AC. Set the BMC jumper to the recovery mode. Power up system and flash BMC from EFI. When done, remove AC. reset the jumper to the normal mode and then re-apply AC.