Install Client Access Server

Installing Exchnage 2010 CAS role on win 2008 R2 (Maillbox and Hub Transport) role is already installed previously

While installing Exchange 2010 CAS role ,getting following error on Readiness checks

Processing object "EXCH2010\owa".
 [2] Unexpected Error
 [2] The path 'D:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\owa' doesn't exist on 'SERVER'.
Parameter name: Path
[2] Ending processing new-OwaVirtualDirectory
[1] The following 1 error(s) occurred during task execution:[1] 0.  ErrorRecord: The path 'D:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\owa' doesn't exist on 'SERVER'.
Parameter name: Path
 [1] 0.  ErrorRecord: System.ArgumentException: The path 'D:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\owa' doesn't exist on 'SERVER'.
Parameter name: Path
 [1] The following error was generated when "$error.Clear();
          $InternalOwaUrl="https://" + $RoleFqdnOrName + "/owa";
          new-OwaVirtualDirectory -DomainController $RoleDomainController -InternalUrl $InternalOwaUrl;
        " was run: "The path 'D:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\owa' doesn't exist on 'SERVER'.


Anyone is having idea why ?

Thanks.