Setting a View's Menu Item to a Sub-Menu
Okay, so if I understand correctly you have a View Page that is part of your main site hiearchy (main menu).  Unfortunately you can only assign a View (at least through the View interface) to a particular menu, but not any of the children of that menu.  This should be a feature request in the Views issue tracker.

What you need to do is go edit the Main Menu through Administration -> Structure -> Menus, list links for Main Menu, and then find your Tasks page that was dropped in their (should be on the first level) and re-position it to where you want it in your menu hierarchy.