I'm one of the developers of BigBlueButton. Did you already install the stub package for OpenOffice.
BigBlueButton has a dependency on OpenOffice, but the following (taken from the documentation) will install a stub page so it won't pull in the rest of the OpenOffice code.
wget http://bigbluebutton.googlecode.com/files/openoffice.org_1.0.4_all.deb
sudo dpkg -i openoffice.org_1.0.4_all.deb
Also, can you check if you already have OpenOffice installed.
dpkg -l | grep office
if so, please remove all the packages, then try following the steps to install libreoffice again. See https://code.google.com/p/bigbluebutton/wiki/InstallationUbuntu#2._Install_LibreOffice
Regards,... Fred