R720 not working with E5-2696 v2

I got a R720 with E5-2640 processors. I want to upgrade to E5-2696 v2. When installing one processor I get the following message before the server power on:
VLT0204 - The system board ... voltage is outside of range

If I try to power on, I get this message:
VLT0304 - CPU ..... voltage is outside of range.

I understand that this CPU is an OEM version, and it's not on the list of supported CPU for R720. However, I see that there are R720 working with this CPU, like here: https://www.ebay.de/itm/DELL-PowerEdge-R720-Server-2x-Xeon-E5-2696v2-12-Core-2-50-GHz-16-GB-DDR3-RAM-/164101285558

This CPU is only 120W. My server has only 1 power source 1100W (not sure if relevant)
This is what I did so far:
- confirm the CPU works fine, in a Precision T3610
- upgrade server BIOS to latest
- make sure the power setting is on Performance 
- use both RDIMM and LRDIMM
- populate more memory slots

Is there anything else I could update or verify? 

Thank you!