Salams Najeeb,
Please check the role assigned to the user, if role is correct check if in the template that role has Add task permission.
Just to note once task is created by anyone other than project owner, it is bound to be approved by project owner to appear for all.
Regards,
Faizan.
Regards, Syed Faizan ur Rehman, CBPM®,PRINCE2®, MCTS