by Marian Vicea.
Hello all!
I had the same problem and I solved it.
It is a bug in BigBlueButton Moodle plugin.
You can fix it by editing the file "view.php" from "mod/bigbluebuttonbn" folder in your Moodle instalation. Just add "$joining = " at line 238 (without the quotes ).
This line should look like this after editing:
$joining = bigbluebuttonbn_view_joining( $bbbsession );
Good luck!
Marian Vicea