The software is looking for a COM port that doesn't exist. Go to Device Manager, find your cable, note the COM number, and manually select that exact port in the Baofeng software's Port menu.
Here are some tips and tricks to help you get the most out of the Baofeng BF-T99 Plus software: baofeng bf-t99 plus software
: Channel 16 can often be designated as a "Scan" channel through the software, allowing the radio to automatically cycle through your other programmed frequencies when selected. Software Compatibility The software is looking for a COM port that doesn't exist