Latest bios there:
https://dlcdnets.asus.com/pub/ASUS/mb/LG…1-ASUS-4101.zip
ASUS X99-E WS does support ECC Reg and latest bios for it can be found there:
https://dlcdnets.asus.com/pub/ASUS/mb/So…S-ASUS-4001.zip
https://dlcdnets.asus.com/pub/ASUS/mb/So…_QVL_160929.pdf
If that helps.
Help will be much appreciated 
@BulldogPO - Sorry, the only thing I know about ECC support is to check to see if it’s enabled in the BIOS or not, and it’s already enabled for this BIOS (Well, set to Auto, not Disabled).
This is normal for many BIOS and ECC usually works, the Reg is the issue here and I don’t think anything can be done by BIOS modding, Asus will have to make you special BIOS by request probably.
If other changes are needed for Reg vs regular ECC, which I assume so, someone else will have to help you, or tell or link me to what needs done, then I can help.
Maybe @dsanke or @chinobino knows what’s needed to enable ECC REG support?
So assuming;
1. He has a Xeon CPU installed
2. The ECC traces are physically connected
3. The BIOS has Registered ECC support enabled
It could be ME FW issue - remember this thread where e97 said;
@chinobino - Thanks! I’ve never seen any BIOS settings for ECC Reg, only ECC support enabled or not. Both these BIOS mentioned here are same/same in this regard, neither have different settings relating to memory anywhere, and both only have ECC Support set to Auto
I checked the ME FW for both, and both are set to C610 - X - High End desktop, so it can’t be this only or both X99-A USB 3.1 and X99-E WS would both support ECC Reg and not just the X99-E WS.
Tonight when I have more time, I will compare both ME FW side by side and see if I noticed any settings that seem related that are not the same.
* Edit ^^ Done, and I see no differences that look like they matter/related ^^ 
Actually I’m still waiting for memory modules to arrive from China.
Latest bios is flashed in and system is working fine with Xeon E5 2640 v3. Currently using 28GB non ECC 3200MHz DDR4 but got concerned about that ECC reg thing. I’ll report back as soon those RDIMM’s arrive 416GB 2133MHz ECC reg.
Indeed they worked flawlessly.
Hi There! I’m a bit of a novice to the HEDT Enthusiast class of hardware and am endeavoring to build a server with a configuration similar to the original poster. Just to get a better understanding of what is being discussed here, there is no physical issue with ECC Reg memory support on the Asus x99-A USB 3.1, correct? I have recently gathered together a rag-tag of PC components including a Xeon E5 2680v4, The aforementioned Asus x99-A USB 3.1, and 64GBs (4x16GB) of 2133MHz ECC Reg Memory. With a flash to the latest bios (likely using a stick of non-ecc memory from another system to flash), will I be able to get up and running with the configuration stated above?
Any information to help advance my understanding of hardware and firmware will be helpful!
Cheers!