Thanks Andy and Leah. The WP_DEBUG has always been on false in the wp-config. So I guess the warning message is critical.
The plugin hasn’t been updated in years, should I manually upgrade to 3.0, then auto update to 3.5.1? Would that make a difference?
Thanks for your help!
forgot to mention: already tried resetting permalinks.
This worked for me:
<a title="" href="https://www.youtube.com/watch?v=VIDEOIDHERE&width=640&height=480">Click to watch</a>
