Thank you for your explanation. It sure caught me by surprise because I have been running the Mindstar GNS 530/430 in my A2A aircraft for about a year with no problem until I recently installed FSUIPC4 to support a new switch panel. I was very happy to find this post with the fix. Now looking back at the GNS product web page I see there is note for FSUIPC users that includes the additions to the FSUIPC.ini file.