Thank you for your reply. I read the advice in the link you provided but:

My system is running Windows 10 and I am using McAfee Internet Security, so Windows firewall is off. I also don't have Internet Explorer but Microsoft Edge (which I don't use). As stated before, the backup worked previously until this morning with the firewall settings I had. There were no changes made to the firewall rules yesterday. Intuit Data Protect is allowed in McAfee Firewall using the designated ports. Also, the ports 80 and 443 are open according to McAfee firewall.