Stored Procedure: Subquery returned more than 1 value
<p>Upon running the sql server it display this error</p>

<blockquote>
  <p>Subquery returned more than 1 value. This is not permitted when the
  subquery follows =, !=, &lt;, &lt;= , >, >= or when the subquery is used as
  an expression.</p>
</blockquote>

<p>Here is the script for my stored procedure</p>

<pre><code>SELECT
  (SELECT SUM(GrossSales)
   FROM cssale
   WHERE EndDate BETWEEN @StartDate AND @EndDate
     AND CashierID = @Employee) AS [Total Sales],

  (SELECT SUM(GrossSales)
   FROM CSSale
   WHERE RefundStoreDate BETWEEN @StartDate AND @EndDate
     AND CashierID = @Employee) AS [Refunds],

  (SELECT SUM(GrossSales)
   FROM CSSale
   WHERE DateVoided BETWEEN @StartDate AND @EndDate
     AND CashierID = @Employee) AS [Voided Items],

  ( SELECT sum(isnull(C.Amount,0)) AS [Discount Amount]
   FROM CSSaleItem B
   LEFT JOIN CSSaleItemDiscount C ON B.CSSaleItemID = C.CSSaleItemID
   LEFT JOIN CSSale A ON A.CSSaleID = B.CSSaleID
   LEFT JOIN CSSaleItemTax D ON B.CSSaleItemID = D.CSSaleItemID
   LEFT JOIN
     (SELECT CSSaleItemID,
             Amount,
             Tax,
             [Type]
      FROM CSSaleItemTax
      WHERE [Type] = 0) AS vsa ON vsa.CSSaleItemID = B.CSSaleItemID
   WHERE A.EndDate BETWEEN @StartDate AND @EndDate
     AND A.CashierID = @Employee) AS [Discount],

  (SELECT CashierId
   FROM cssale
   WHERE EndDate BETWEEN @StartDate AND @EndDate
     AND CashierID = @Employee)AS [Cashier]
</code></pre>