We running 2 application on amazon ec2 (backend.abc.com & frontend.abc.com). For that application, we used a paid SSL Certificate. That
We have the same error. For solving your issue update your "SSLCertificateChainFile" with the newest version of your trusted SSL site. In our case is comodo.
You need to go to your trusted site and find under your certificates the "CA-CRT". Copy the content.
If you can't restart apache the easy way is reboot your instance.