The version on you Moodle 2.9 may be OK as it is good for production in most cases. There are some edge cases that were fixed in the last two releases, but if you don't hit them, you are good. Here are the changes per version.
Now getting back to your problem on Moodle 2.5, is that message coming when you launch into the meeting? do you have any particular configuration of that activity? Lets say, wait for moderator, open in a new window etc. And lastly, if you turn on the debugging messages, what is the full message that you receive?