Hi Paul,
Could you please provide the name of the application\program that is causing the issue?
COM3 is generally taken up by an internal dial-up modem as its main communication link to the Internet.
I would request you to please provide us a screenshot of the issue you are experiencing to get a better understanding of the issue.
How to include a screenshot in your post:
Please get back with more information on the issue so that we may assist you better.