Good afternoon.

I have a Dell PowerEdge T310 running Windows 2008 R2 server.

It came with 2 x 2GB 1333Mhz Unbuffered memory sticks.(Total 4GB)

I added 2 x 2GB 1333Mhz Unbuffered memory sticks and it worked fine giving me 8GB total memory.

Last week I bought another 2 x 4G 1333Mhz Unbuffered memory sticks, to make it 16GB total, using all the 6 (six) slots available on the Intel XEON based motherboard.

Now, the server will not start and gives me a memory error on the front screen.

If I take out 2 sticks, using only the new 2 x 4GB and the 2 x 2GB memory stick the server will start with no problems.

I am looking for answer on "why" it will not work with 4 x 2GB and 2 x 4GB sticks using all 6 (six) available slots. 

I am wanting as much memory as possible and to utilize all the 6 slots.

I can purchase 6 sticks of "registered" memory, but if that will not working either I am hesitating the purchase.

Any help would be greatly appreciated.

(Browsing Amazon, I do find a kit of registered models that they say will work being Dual Rank and having the ability to use all 6 slots:  

24GB KIT (6 x 4GB) For Dell PowerEdge Series M610 (ECC Registered T310 (ECC Registered). DIMM DDR3 ECC Registered PC3-10600 1333MHz Dual Rank RAM Memory. Genuine A-Tech Brand.