I honestly have no idea. If Windows’s Device Manager reports it found USBasp and there is no question mark or acclamation mark, it means the device driver is installed correctly. Did you click on ‘Detect Device’ before ‘Upload Firmware’? Since you already know you have OS 2.1, you can skip ‘Detect Device’, just simply select OpenSprinkler_v2.1 from the dropdown list and click on ‘Upload Firmware’ (assuming the device is in bootloading mode prior to clicking on ‘Upload Firmware’).