Must declare the scalar variable @PR_Name

exec sp_Select_Building_FlatNEW 1,1                                
 select @UserNames =UserName    
    
  if exists (select * from sysobjects where xtype='u' and name='#flnDtls')    
  begin    
  drop table #flnDtls    
  end    
      
  create table #flnDtls     
 (UserNames nvarchar(max),    
 Flat_No varchar(50),    
 Flat_Id int,    
 PR_ID int)    
      
  insert into #flnDtls exec sp_Select_Building_FlatNEW @SC_ID,@Flat_Id    
      
  select * from #flnDtls    
  --declare @sss nvarchar(max)    
  set @PR_Name = (select Top 1 UserNames from #flnDtls)    
  print @PR_Name    
      
if(@Quat=1)                
begin               
set @sql='SELECT DISTINCT       
                      dbo.iBillHead.BillHeadName, dbo.Society.SCName, CONVERT(varchar(500), dbo.Flat.Flat_No) AS Flat_No, dbo.Building.Building_Name,       
                      dbo.Flat.Flat_Area, dbo.TransMember_BillHead.Trans_Bill_Quat AS Amount, dbo.Building.Building_Id, dbo.Bill_Generation.Bill_No, CONVERT(varchar,       
                      dbo.Bill_Generation.Bill_Date, 103) AS BillDate, SUBSTRING(DATENAME(m, dbo.Bill_Generation.Bill_To_Date), 0, 4) AS FromMonth, SUBSTRING(DATENAME(m,       
                      dbo.Bill_Generation.Bill_From_Date), 0, 4) AS ToMonth, dbo.Society.SCRegDate, dbo.Society.SCAddr, dbo.Society.SCRegNo, dbo.Flat.Flat_Id,       
                      dbo.Bill_Generation.Bill_Id, dbo.Bill_Generation.Total_Amount AS Total, dbo.Bill_Generation.Pending_Amount AS pending, dbo.Bill_Generation.Bill_To_Date,       
                      dbo.Bill_Generation.Bill_From_Date, dbo.Bill_Generation.Due_Date, dbo.Bill_Generation.LateCharge_Amount, dbo.Bill_Generation.Discount,       
                      dbo.Bill_Generation.Bill_Date, dbo.Bill_Generation.Arrears, dbo.Bill_Generation.Grand_Total, dbo.Bill_Generation.Principal_Amount , @PR_Name as Username    
FROM         dbo.Member INNER JOIN      
                      dbo.Society INNER JOIN      
                      dbo.Flat INNER JOIN      
                      dbo.Building ON dbo.Flat.Building_Id = dbo.Building.Building_Id INNER JOIN      
                      dbo.Member_Flat ON dbo.Flat.Flat_Id = dbo.Member_Flat.Flat_Id ON dbo.Society.SC_ID = dbo.Building.Soc_Id INNER JOIN      
                      dbo.iBillHead INNER JOIN      
                      dbo.TransSoc_BillHead ON dbo.iBillHead.BillHeadID = dbo.TransSoc_BillHead.Trans_BillHeadID INNER JOIN      
                      dbo.TransMember_BillHead ON dbo.iBillHead.BillHeadID = dbo.TransMember_BillHead.Trans_BillHeadID ON       
                      dbo.Society.SC_ID = dbo.TransSoc_BillHead.Trans_SC_ID ON dbo.Member.PR_ID = dbo.Member_Flat.PR_ID AND       
                      dbo.Member.PR_ID = dbo.TransMember_BillHead.Trans_Member_ID INNER JOIN      
                   dbo.Bill_Generation ON dbo.Flat.Flat_Id = dbo.Bill_Generation.Flat_Id      
            

end            
            
exec(@sql)