Yep, i had it twice and it was the problem.
I've retested using
echo tep_draw_checkbox_field('instock', 1, false, 'onClick="this.form.submit()"') . HEADER_INSTOCK . '<BR>' . "\n";
instead of
echo tep_draw_checkbox_field('instock', 1, false, 'onClick="this.form.submit()"') . HEADER_INSTOCK . '</form></td>' . "\n";
(as it apears in the addon files)
and IT WORKED! I must of written something wrong in the code last night because all it did was to mess out the layout..
Thank you very much mdtaylorlrim!
LE: If i click on a category it doesn't display the filter, it will only show up if i select to show only a manufacturer, it won't show up if i select all manufacturers. Can this be easily changed?
Maybe the autor of the addon reads this post and modifies the files posted in the addon.