I think you need to change the string so that the variables are evaluated, like this:
PHP Code:
$order = '<td class="alt2">
<form action="misc.php?do=points_usergift&giftid='.$resultgift[giftid].'&pointgift='.$resultgift[giftpoints].'" method="post">
<input type="hidden" name="s" value="'.$session[sessionhash].'" />
<input type="hidden" name="securitytoken" value="'.$bbuserinfo[securitytoken].'" />
<input type="hidden" name="do" value="points_usergift" />
<input type="submit" class="button" value="submit" />
</form></td>';
(the changes are around $session[sessionhash] and $bbuserinfo[securitytoken]).
Also, is that the entire plugin code? If so, you should really check $_REQUEST['do'], otherwise you will interfere with other functions in misc.php (but maybe you only posted part of the plugin).