Plug and Play Configuration Error after Updating RAID Firmware - PE2450 now won't boot!

I have an old PowerEdge 2450 server with a PERC 3/si RAID controller.  I just updated its firmware upon finding it was ancient (2.1.x) to the latest 2.8 firmware from Dell's website.  I had to do so from floppy disk, since my version was too old to use the Windows-based firmware

Upon rebooting, I get a "Plug and Play Configuration Error" right after the system detects its dual-P3 1GHZ processors.  I have shut the system down and used the ISACLR jumper to clear settings as described, and reset them; this does not help.  I have turned off serial, and parallel ports.  I have removed the backplane (which contains a 3Com gig NIC based on a Broadcom NetXtreme chip, the onboard NIC is disabled); this does not help.

I'm unsure where to go from here.  The server will not boot now; it halts at the error message, only allowing me to go into setup.  The firmware upgrade was uneventful with no error messages of any kind.  If someone could help me out with this, I'd really appreciate it.