How come I can't see the Global Settings tab under My Account?

In OpenX 2.6 a logged in user is able to switch between account types. Inventory can not be owned by an administrator account type, but only an admin can view the Global Settings tab.

If you have logged in as a user with administrator account permissions, you might be set to 'Working as->Manager' so that you are able to modify inventory.

If you wish to then check Global Settings, you should click on My Account and then, at the top right, set 'Working as->Administrator' so that the Global Settings tab is available.