I found this on the Intel web site:
After flashing the Intel® Desktop Board D850GB BIOS, you may get the following message:
CMOS/GPNV Checksum Bad
Press F1 to Run SETUP
This is caused by a change to the CMOS map between BIOS versions. Press F1 to go into SETUP, and then either press F10 (to Save and Exit), or follow the "Resetting CMOS After Upgrade" instructions (in the General Instructions: BIOS Upgrades section). This will align the CMOS map for the currently installed BIOS.
This applies to:
Intel® Desktop Board D850GB
This may be valid for other motherboards as well.