This also happened to me when I tried to install community builder 1.7.1 on a Joomla 1.7.3. I had a backup of the site when it was in 1.7.2 so I reverted to that and then installed community builder 1.7.1 and it worked fine without errors. We host all of our own websites on our internal Ubuntu Linux Servers running PHP 5.2.x

Just wanted to reply in case anyone else is seeing this.