It could also be your network settings (router), are the ports open so you can send, and person you are sending to is he/her behind a firewall and can they receive files from other persons ?
I would definitely try to uninstall Mcafee, not just disable it, and make sure it´s gone, Norton Internet security some versions ago, continued to be installed and block access to certain even through you uninstalled it (it was preloaded with a laptop), search for the files in the windows drive. Also get another antivirus, there are much better options out there and for free smile https://www.av-comparatives.org/consumer/