the problem was the form action:
<form action="" method="post" enctype="application/x-www-form-urlencoded" name="frmOrganisations" id="frmOrganisations">
in a plugin page, the action should not be left blank, it should use the PHP Self variable to post to the plugin page:
<form action="<?php echo (htmlentities($_SERVER["PHP_SELF"], ENT_QUOTES)); ?>" method="post" enctype="application/x-www-form-urlencoded" name="frmOrganisations" id="frmOrganisations">
you had also left the checked value for the checkbox blank.
i corrected that by changing the checked value to 1.