exact memory spec for netserver lt6000r

[CA827864]

Hi,
I am trying to determine exact memory spec for our LT6000r netserver. On the HP web site, it says "133MHz" and "ECC". It does not say "Registered ECC" or "Buffered". It just says ECC.
Am I to assume that it should be "Registered ECC"?
I noticed that original memory that came with the server had "128MB 133 Reg Ecc", but why does the HP web site just says ECC?
I tried a pair of memory modules that say 133MHz and ECC but they don't seem to work. It sees the size when booting up and does not seem to use it. If I take out the original memory and use only the 133MHz and ECC memory modules, the server doesn't even boot.
Can someone tell me exact spec for the memory module?
Thank you
Paul

[CA660377]

168 pin PC 133 ECC Registered SDRAM 3.3V with SPD