Help - Sales Stage Id Field Validation

Hello,

We have a requirement to restrict certain role based users  from closing a deal. In other words display an error message when the user picks sales stage as "Closed/Won". Here s what I tried

([<SalesStage>] = "Closed/Lost" OR [<SalesStage>] ="Negotiations Taking Place" OR [<SalesStage>] = "Financial Approval Pending" OR [<SalesStage>] = "DO Received")  and (UserValue('<Role>') ='Partner Sales Representative Role')

This works fine as long as the user toggles betwenn sales satges other than "Closed/Won". But once he picks "Closed/Won" the error pops up as it should but doesn't go away when he picks any other options. The message keeps popping up .