4Rx4 memory with 2Rx4 memory? Incompatible?

Hello all

I have a Dell R710. We recently upgraded the memory and added 6 matching 16GB modules. All was well. DIMM were purchased off of ebay to save money... bad idea...

However, here we are... 1 of the 6 modules was bad. So I ordered a new one (from differnt source). As soon as I put it in, the server will not even POST... 

If I remove the module, server boots fine - yes it complains that the memory should be in, and disabled that bank (so if A3 is missing, A6 and A9 are disabled).

One more order... same thing.. This time I tried to match the frequency and that it was low voltage. Again, same thing... Server wont even post.

Only difference I see now is that the current memory is showing 2Rx4, while the new one is 4RX4.

Are they incompatible? Do I need to order the 2RX4 low voltage memory?