Question:

Why a System Administrator cannot use Vault Loader?

Answer:

An Administrator may not have all necessary permissions. For Vault Loader (and other similar permissions), the permission needs to be specifically assigned in order to use.

Note: System-provided permission sets cannot be modified.  A user that is an admin and has the desired permission assigned needs to add this permission.  A Vault Owner can do the assignment, as most permissions are associated with that account.

1. Navigate to: Admin --> Users & Groups --> Permission Sets. 
2. Hover over the System Administrator Actions.
3. Click the Action Icon (gear icon) next to System Administrator Actions, and select Make a Copy.

4. Name and describe the new Permission Set as desired, and click Save.
5. Click on the newly-created Permission Set.
6. Click the Application tab.
7. Click Edit in the upper-right corner of the screen.

8. Scroll down to the Vault Owner Actions, and enable (check) the box under Vault Loader.

Related Documentation:

Vault Help Documentation: About Permission Sets

Thank you