If you check your System Status page on MythTV and see “FAILED: XMLTV returned error code 1” makes sure you have symlinks in /home/myth/.mythtv/<XMLTV Config file> to where the files truly exist.

Why: mythtv-backend runs mythfilldatabase when needed but it runs as the user “mythtv”, not the user you set everything up in, as for me – “myth”.  My “Comcast 0.xml” files were in my user account.  I created symlinks as shown below and then let mythbackend run as needed and all is better now.

$ channels -> /home/myth/.mythtv/channels/
$ Apr 21 10:33 Comcast 0.xmltv -> /home/myth/.mythtv/Comcast 0.xmltv
$ Apr 21 10:33 Comcast 1.xmltv -> /home/myth/.mythtv/Comcast 1.xmltv
$ Apr 21 10:33 Comcast 2.xmltv -> /home/myth/.mythtv/Comcast 2.xmltv
$ Apr 27 2016 config.xml -> /etc/mythtv/config.xml

When it works your status screen should look like this (sorry, no before screenshot when it had the error,  oops!)

I had googled for “xmltv returned error code 1” and all I could find was crap posts with no solutions.  Hopefully, this will help someone else.