|BIOS checksum error related to changed hardware.|
The BIOS checksum is build by the settings and the installed hardware. If another hardware is installed and not correctly set in the BIOS, the checksum is different and you'll get a checksum error.
The same happens, when battery gets empty.
The former known hardware informations gets lost and the standard settings are set automatically.
Plug and Play recognizes new hardware builds a checksum, compares the checksum with the checksum of BIOS settings, recognizes that they are different and you get a BIOS checksum error.