DL1850R memory problem

[Geerts Nick]

We have a DL1850R server reporting correctable memory errors so we'd like to replace the 256 MB 100 Mhz Dimms actually in place (the manual prescribes 100Mhz registered SDRAM 72-bits wide ECC). We found memory we tought being of the same type in a DL580G1 (indication on the memroy is 256MB, Sync, 100 Mhz, CL2,ECC) but when we put it in the server the server does not start. Why is this memory not compatible?

[e4services]

Micron shows:
Compaq ProLiant 1850R 6/600..SDRAM, PC100 CL=2 ECC Registered (317749-001 $220)
Compaq ProLiant DL580..SDRAM, PC100 CL=2 ECC Registered(170514-001)
Interesting that they do not show as different parts, but the 1850R may be some proprietary thing on it, do not know for sure.
Are you sure that you have the memory seated correctly? that would stop the POST.
Tried another slot?
But the wrong memory will also stop POST