Dell R720xd Restart on Memory Error

Sometime there could be issue with DIMM slot. As you already replaced DIMM with another slot and still see the error, you can check by not installing DIMM on A2 and B2 and see whether that make any difference.

You can also check with one CPU and install DIMM in A1 slot only and check the behavior. If it works you can add second CPU and DIMM in B1 slot and check it. after that you can add one DIMM to each CPU and see where it is failing. 

Did you have latest BIOS and iDRAC FW installed on the server? If not can you install latest FW and monitor the behavior.

Thanks for replying when system re power on every thing looks fine but after sometimes or someday the error automatically comes and system restart and halt on this error you can see this log pic last error comes on 31-Oct then comes 08-Nov.

Today it comes three times

from 31-Oct to 8-nov Server work fine no error comes.

yes latest i shared the pic o

As it is showing machine error on CPU 1 also this could be some issue with motherboard. You can try with one CPU and one DIMM on A1 slot and check the behavior to see whether DIMM B2 slot creating any issue