I am attempting to upgrade to Fldigi ver 4.1.20. When I try to open it after download I get the following message "Fldigi ver 4.1.20 cannot be opened because of a problem". I am using a 2010 Mac Book running High Sierra 10.13.1. Have tried reloading several times with no luck. I have been running 4.1.16 with zero trouble. I have upgraded Fldigi steadily over the last 4 years or no with no trouble. Can anyone help?