I can't add a custom field?

I can't add a custom field?

I am trying to add a field onto the Leads page, the details of it are below;

Label: State
Section Name: Lead Information
Length: 20
Also create for: Nothing

Upon clicking save I get a message: "Field in the specified label already exists for Leads"

I know for a fact there is no field in Leads called "State". I have looked on the edit fields page, as well as edit layout page.

This is not the first time a message like this has come up.

Can I use a field, called "State", in the Leads page?