Error:The CALC command [IF] can only be used within a CALC Member Block Rule

Hello,

Below is my calculation script and when I try to validate it, I am getting

 A validation error was received from the Planning server.

'Error:The CALC command [IF] can only be used within a CALC Member Block Rule DGAGL.DGAGL.DGAGL.SCRIPT.01.Controler_Level0'

Can someone please give some suggestions ?

   IF( NOT ( @ISLEV("Entity",0)) )

        @RETURN(@CONCATENATE(@CONCATENATE(@CONCATENATE(@CONCATENATE("Cannot select (",@ALIAS(@CURRMBR("Entity"))),"). Select Entity. | selected group ("),@ALIAS(@CURRMBR("Entity"))),"). Please select a specific entity."),ERROR);

     ELSEIF( NOT ( @ISLEV("Niveau",0)) )

        @RETURN(@CONCATENATE(@CONCATENATE(@CONCATENATE(@CONCATENATE("Cannot select (",@ALIAS(@CURRMBR("Niveau"))),"). Select Entity. | selected group ("),@ALIAS(@CURRMBR("Niveau"))),"). Please select a specific level."),ERROR);