Multi-part .rar files (like part01 , part02 , etc.) are split archives. You cannot open a single part like part04.rar on its own.
: Ensure you have downloaded all preceding parts ( part01 through part03 ) and any subsequent parts for that specific firmware version. Download LLOYD GL40HOBOZS Software USB part04 rar
: Place all parts in the same folder on your PC. Multi-part