Well from a coders perspective, i would propose:
1. UserManagerNewEdit.png
2. User_Manager_New_Edit.png
3. UserManager_NewEdit.png
4. UserManager.NewEdit.png
5. UserManager_NewEdit.png
6. User_Manager.New_Edit.png
7. User.Manager_New.Edit.png
Why so many differnent?
Explaination:
The Component -> User
The Task -> Manager
The Action -> New & Edit
I would prever #7 : it states clearly that we are doing some with the user, managing him and editing/make a new one.
Left side is User.Manger - right side the New.Edit
This could be taken for all. e.g.:
Template.Manager_Toolbar.png
Trash.Manager_Menu.Items.png (well here is not really a task, therefore it could also be: Trash.Manager_Menu_Items.png [#8]).
Ahh, it could be also: trash.manager_menu_items.png (all lower letters)
I leave it up to you now to find the best solution

=> 16 possibilities.