It looks like your web server sucks and you should fix it.
At present, there is no config way of reducing the yui_combo length parameter, but it can be done by making a minor modification to core code.
See http://yuilibrary.com/yui/docs/api/classes/Loader.html#property_maxURLLength for information on the parameter. From memory, you will need to open lib/outputrequirements.php and find the constructor for the page_requirements class.
Add a new setting to $this->M_yui_loader for maxURLLength and set it to something lower:
$this->M_yui_loader = 768;
Please note, you're using an older version of Moodle which is no longer supported so I may be a little off with my recommendation here.