Right, it's what I thought then, your host is disabling access to it, so you'll need to ask them. Who do you host with?
why it is not allowing to change permissions for task.php file ???????? Any Idea guys.......
Because of the reason I just gave you above, your host is disabling access to it. Often on free hosts, when they detect a script is using "too many resources", they force the permissions to 000 and stop you changing them.