HP Proliant ML150 G6 not using all installed memory

[Bynan]

I have a client with an HP Proliant ML150 G6.  It had one proc and 16GB of RAM.  They wanted to upgrade it to get a little more life out of it.  So, I had them order the second proc and 32GB of RAM.  I installed everything, and the second proc shows up fine, but the system gets a "101-Unsupport Memory Population" message from the BIOS on boot, and Windows now says "48GB (24GB usable)".

Any ideas why the other 24GB is not usable by Windows?

[waaronb]

How is the memory split up between the processors? It's generally best to install memory equally across CPU's, but that's a general preference.

Here's the quickspecs for the server. Page 29 has the memory population guidelines:
http://www8.hp.com/h20195/v2/GetDocument.aspx?docname=c04285936

A lot of it depends on the size and rank of the memory... quad ranks are different than double, etc. It's hard to give a good answer without the specifics of each memory module, but with the quickspecs in hand, you can probably figure out if something not installed in the right way.