If you checked the firmware folder of BioStar 2 on a recent release (C:\Program Files\BioStar 2(x64)\firmware) , you may see that the firmware have a _sign at the end of the file name.
This is a code signing security feature implemented to avoid malicious users applying their own firmware to the device.
This means that you cannot upgrade or downgrade the device firmware to any other firmware that doesn't have the same Suprema code signing once it has a signed firmware.
Note that all new devices would already have code signed firmware mounted on the device.
If you happen to have a customized firmware in the past which does not have code signing, please contact us to have your firmware code signed.
Else the firmware upgrade will fail on new devices with code signed firmware.