This is usually a COM port mismatch. Ensure the software settings match the COM port number in your Windows Device Manager.
However, owning a GM339 in the modern era comes with one significant hurdle: Unlike modern radios that use USB plug-and-play, the GM339 requires a specific legacy ecosystem of software, cables, and operating systems. motorola gm339 programming software
: You generally need a CPS version that is equal to or higher than the version last used to program the radio. For example, if the radio's codeplug (CP) version is R7.01, you would need Professional CPS Version 7.01 or later. This is usually a COM port mismatch