rx2600: DRAM Failure on DIMM1B

[Learn_1]

we have rx2600 running windows2003 enterprise edition.recently after restart the system is reporting the following error.
"Start memory Discovery
DRAM Failure on DIMM1B Deallocated rank
No Memory foung
Cell Halt"
i have tried by swapping the memory module with another that was being reported(1B). I have also tried by installing on other slots of this bank but on whatever slot of this bank i install DDRAM it reports memory installed on that slot as failed.The DDRAM is of 266 MHZ and is of HP Part.
Can anyone suggest further diagnostic and guidance or will i have to replace the system board?
Also if anyone can suggest or forward detailed manual of using EFI promt for remote management.
Thanks