error: Only one expression can be specified in the select list when the subquery is not introduced with EXISTS

I get the error "Only one expression can be specified in the select list when the subquery is not introduced with EXISTS" when I execute this code in SMS:
select v_R_System.Name0 from v_R_System where v_R_System.Name0 not in (select v_R_System.Name0, v_R_System.User_Name0, v_gs_environment.VariableValue0 from v_gs_environment JOIN  v_R_System ON v_GS_environment.ResourceID = v_R_System.ResourceID where v_gs_environment.Name0 LIKE 'War%')

the subquery works on it's own.
I'm trying to determine which computers do *not* have a particular environment variable on it.Start Free Trial