In order to reset the inventory, your user need to be put as a manager at the administrative settings.
If you are not put as a manager there, you can only see the physical value of the inventory, not the scriptical value and you can not reset the inventory.
In order to check this, you will need to go to Account settings.
And click on the Company Settings tab.
From here, you will see on the right side: Administrative Settings and below, the Managers.
Click on the user that you want to set as a manager and then Save the changes.
