Today I upgrade to the latest version of Responsiviser for Joomla 2.5 and it will not resize videos to fit on the screen of a mobile device like an Android phone. Sometimes you can double-click on the video and it will resize to full screen, but that is not an acceptable solution. Besides, it does not work every time.

Additionally, you will see an error message that is now appearing on our website since I upgraded to the 2.4.2 build.

The issues are:

1. How do we get videos to resize to fit the screen

2. How do we get the error message on our site removed. (url: www.sportszone123.com).

Note: When I turn off the plugin called "System - Responsiviser Template Switcher", the desktop display returns to normal without an error message, but we do not have a responsive mobile site for devices.

First of all you forgot to disable the 'Debug mode' of Responsivizer
That's why you get debug warning messages, so turn it off immediately

After that, you are using av Player /JWPlayer for videos and it's not mobile ready
It render videos with fixed 510px width so videos won't scale.
2 options:
1. Find a version of that module that is mobile ready supporting fluid videos
2. Assign responsiveness to div.jwplayer and div.avPlayerContainer
There is a parameter in Responsivizer named 'Responsive elements selectors', if you add:

div.jwplayer, div.avPlayerContainer

that should do the trick.