(For my own benefit also) In trying to aggregate some of the web servers I have deployed in VMs, I managed to break KnowledgeTree and had to re-install. On Ubuntu, it's a real P.I.T.A. At one point, I couldn't get past the following error:
Warning: include_once(DB/.php) [function.include-once]: failed to open stream: No such file or directory in /usr/share/knowledgetree-ce/thirdparty/pear/DB.php on line 371
The fix for the above is easy. It's usually an indication that there's extra kruft in the config-path file. To fix it, delete all of the lines in /usr/share/knowledgetree-ce/config/config-path except for /etc/knowledgetree-ce/config.ini.
Also, if you're working with the Chrome browser, you'll probably get into the condition where "control.php" downloads instead executing on the server. The point to remember is that even if you fix it, this condition will continue until to erase your browser history.
Yeah, it's been that kind of day.