The first 2 errors are telling you that you could not execute a session_start() because headers were already sent due to output being generated at the files/line-numbers listed at the end of each error. Of course, a script being run via cron probably has little/no use for sessions in the first place, I would think. Possible fixes would be to get rid of the session_start()'s if you don't really need them, use output buffering (see [man]ob_start/man), or find out what is generating output and stopping it from doing so.
I'm guessing that the last error is a symptom of a command line PHP script being run from the directory where it was invoked, not ncessarily the directory where the PHP file "lives", so the relative path may not be pointing to where you think it is. You could make it change to that directory within the script by adding the following to the start of the script:
<?php
chdir(dirname(__FILE__));
