Poweredge R710 Memory Upgrade Configuration

Hi,

I've got a Poweredge R710 that currently has 32GB RAM installed via 8 x 4GB modules. I've just ordered a 32GB upgrade (2 x 16GB) from Crucial to bring the server up to 64GB in total, however no matter what configuration i put the modules in, the server just reports an invalid or non optimal configuration.

Can someone help me work out the correct configuation please?

Thanks,
Andrew