Trying to set up workflow to prevent users (except Administrator Role) from updating an Opportunity

OK, here is the rundown,

 

I have created a workflow to prevent users from modifying an Opportunity once the Opportunity has been closed (Won or Lost) by using the following criteria:

 

Record Type

Opportunity

Trigger Event

Before modified record saved

Criteria = [<StageStatus>] = 'Open'

Actions If Condition Is False

Cancel Save [Checked]

Display Message

Closed Opportunities cannot be reopened/reused. Please create a new Opportunity to continue.

 

This Criteria works, and once an Opportunity is closed, The Stage Status is no longer "Open" creating a False condition...and no changes can be applied to the record. The Display Message appears as expected.