Poweredge R510 only recognizes 32Gb RAM (of total 64Gb)

Hi there,

I have  a R510 poweredge server with 1 processor (Intel(R) Xeon(R) CPU E5630  @ 2.53GHz)

It used to have 12Gb (3x4Gb) of ram, but i've decided to do an upgrade.

I have purchased these modules: 

8 x 8GB PC3L-10600R DDR3 1333 ECC Reg, that is a total amount of 64Gb

Unfortunately, the system recognizes only the 32Gb.

I have also tried to use just the 4 modules on the slots next to the empty cpu slot, but the system didn't boot cause it couldn't see any ram installed.

Can you please help?

Thank you in advance.