Using several subqueries in sql statement

I am trying to use several subqueries but I am getting an error. It works if I remove the second subquery.

Error: Msg 512, Level 16, State 1, Line 2 Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

USE SUPERSTARIS
SELECT lines.Item,
       Inventory.ItemAlternative,
       Inventory.OnHandPhys,
       Inventory.Allocated,
       Inventory.CostPrice,
       replace(vInventoryOptional2Values.Value, '/', '') AS Brand,
       Inventory.Optional3 AS StockStatus,

  (SELECT SUM(l.Invoiced) * -1
   FROM lines l
   WHERE l.Date >= '2014-01-01'
     AND l.Date <= '2014-01-31'
     AND l.Item = lines.Item) AS QtySoldInPeriod,

  (SELECT SUM(lines.AmountBase-lines.CostAmount)*-1
   FROM lines l
   WHERE l.Date >= '2014-01-01'
     AND l.Date <= '2014-01-31'
     AND l.Item = lines.Item) AS QtySoldInPeriod2
FROM lines
INNER JOIN inventory ON lines.item = Inventory.item
INNER JOIN vInventoryOptional2Values ON Inventory.Optional2 = vInventoryOptional2Values.RecordID
WHERE lines.Invoiced < 0
  AND Inventory.Status = 0
  AND Inventory.Optional3 <> 3
GROUP BY Lines.Item,
         Inventory.Optional3,
         Inventory.ItemAlternative,
         Inventory.OnHandPhys,
         Inventory.CostPrice,
         vInventoryOptional2Values.Value,
         Inventory.Allocated