Hi!
Ubuntu's dotlrn package is a very old version (2.5.0), and it is probably uncompatible with "recent" versions of postgres (>= 9).
There is work ongoing to fix this situation and update all the openacs/dotlrn stack in Debian/Ubuntu, including a naviserver package, openacs 5.9.1 and probably a new dotlrn package dependent on the latter, but, until this is done, the best way to install an up-to-date dotlrn in Ubuntu is using the installer:
https://openacs.org/xowiki/naviserver-openacs
After installing OpenACS, it is possible to install the dotlrn packages directly from the "Install from Repository" page, pointing a browser to "/acs-admin/install/" in your instance.
Kind regards,
Héctor
