Clasification with Document Properties

Hi,

I´m stock in creating a Clasification for my Documents, I have added in the System Administration -> System Configuration -> Knowledge Management -> Configuration

-> Content Management -> User Interface -> Search -> Search Options Set > UISearch > 'Allowed Sort Properties'

the property Departamento as mandatory and indexable..... , and when I try to modify a document (i.e the description) then it sends this error message

"Enter values for these mandatory properties: Departamento"

But I can not see the property.

I´m alittle confused on how to assign new properties to a Document and then with this properties Clasificate in Catgegories de Documents.

Can some one guide me throug this process?

Thanx in Advanced!

Gerardo J