I checked everything...I checked their group and saw that they can edit their own posts but users are still saying that they can't edit their own posts....
Did you change Edit Time Limit in Configuration -> Posting?
Upload xmlhttp.php file in your forum's root.
Edit time limit: 0
And Yaldaram: Here's part of it...
...
else if($forum['open'] == 0 || $forumpermissions['caneditposts'] == 0 || $mybb->user['uid'] != $post['uid'] || $mybb->user['uid'] == 0)
{
xmlhttp_error($lang->no_permission_edit_subject);
}
...
nvm, it was a plugin conflicting with it. Thanks!