Just a note in case anybody is looking for this. Have an old Dell R410 that was rebranded for Fortinet. The BIOS was stuck at an old version so I downloaded new version, FreeDOS formatted a bootable USB stick with UNETBOOTIN and tried installing update but got the following error:
Googled around and found https://blah.cloud/hardware/flashing-over-oem-r-biosfirmware-on-dell-hardware/
Solution is to run the command like this:
BIOSFILENAME.exe -wipeclean -forcetype
Hope this helps somebody else trying to find this.