SQL 2005 - permissions - remove button greyed out

Hi-
SQL 2005 - sp1
When I look at the Permissions *** of a table's properties and select a
User the 'Remove' button is greyed out, therefore not allowing me to remove
that user, I am logged in as sa.
Can anyone shed any light on how to remove a user or role from a table using
Management studio?

Thanks.


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