I have 3 4GB for each processor. 6 in total (24GB). Whit Optimize Mode in BIOS (ver. 3.0.0).

I try install only 2x16GB and work fine.

But if i try as you suggested A1,B1 > 16GB and A4,B4 the server show me this message:

(the server ask me to press F1 to continue, and it's boot up correctly. But I don't want to proceed with 'Unsupported memory configuration')

Same message if i try A1,B1 > 16 Gb A2,B2 > 4GB A3,B3 > 4GB

I have 3 4GB for each processor. 6 in total (24GB). Whit Optimize Mode in BIOS (ver. 3.0.0).

I try install only 2x16GB and work fine.

But if i try as you suggested A1,B1 > 16GB and A4,B4 the server show me this message:

(the server ask me to press F1 to continue, and it's boot up correctly. But I don't want to proceed with 'Unsupported memory configuration')

Same message if i try A1,B1 > 16 Gb A2,B2 > 4GB A3,B3 > 4GB

Thanks for the reply. It's a ESXi 5.5 server so I have to use the "Non-Packaged" solution to update the bios (I found the link below). Or is there another option for ESXi hosts?
 
BIOS LINK.
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=VX07C&fileId=3287631725&osCode=WS8R2&productCode=poweredge-t610&languageCode=EN&categoryId=BI

Unfortunately the memory in my possosso not DELL:

Kingston KTD-PE3138LV/4G -> 4GB 1333MHz Reg ECC x8 Low Voltage Module 2R
Kingston KTD-PE313LV/16G -> DDR3L, 1333MHz, ECC, CL9, 2R, X4, 1.35V, Registered, DIMM, 240-pin

Hi Trish,

I updated the bios at 6.4.0 but warnign was not removed. And after apper the message Strike F1 to continue.. I try the suggest configuratio 16+4 for the first channel.

It is possible that the two types of RAM are not compatible? Or is there some configuration to be set in the bios?

Thanks in advance.

All channels and banks have to match. Also, what you put on one CPU , you have to have on the other. You will have to remove 4 of the 4GB Dimms.

Your Only Option is 

CPU 1 

A1 - 16 gb

A4 - 4 gb

CPU 2

B1 - 16 gb

B4 - 4 gb

yes, this is the configuration that I tested