I'm getting the following error message when I go to "Player management > Create a new player" (after entering the player details)...
"Make sure to use a callable validation!"
Here's what I've determined so far...
1) SERVER ITSELF IS OK
I installed a second copy of WordPress into a sub-directory on the same server (with default theme installed). I then installed JW Player and I was able to do all tasks fine (including creating a new player). So I know the server is capable of running the plugin.
2) THEME AND PLUGINS OK
I then went back to my main WordPress installation, and disabled all plugins (except JW Player). I also switched the theme back to the default theme. But I'm still getting the error message when I attempt "create a new player".