Syntax Error Converting Datetime From Character String (2000)

i have a stored proc running against the Northwind DB




Code Snippet
CREATE PROCEDURE CustomPaging
@intOrderID varchar(10),
@strCustomerID varchar(10),
@intEmployeeID int,
@dteOrderDate datetime,

@startRowIndex int,
@maximumRows int,
@SortOrder int
AS


DECLARE @TempItems TABLE
(
ID int IDENTITY,
OrderID int
)
DECLARE @maxRow int
SET @maxRow = (@startRowIndex + @maximumRows) - 1
SET ROWCOUNT @maxRow
INSERT INTO @TempItems (OrderID)
SELECT OrderID
FROM Orders o
INNER JOIN Customers c ON c.CustomerID = o.CustomerID
INNER JOIN Employees e ON e.EmployeeID = o.EmployeeID
ORDER BY CASE @SortOrder WHEN 0 THEN OrderID
WHEN 1 THEN c.CompanyName
WHEN 2 THEN e.FirstName
WHEN 3 THEN o.OrderDate
WHEN 4 THEN o.RequiredDate
WHEN 5 THEN o.ShippedDate END

SET ROWCOUNT @maximumRows
SELECT o.OrderID, CompanyName, e.FirstName + ' ' + e.LastName EmployeeName, o.OrderDate, o.RequiredDate, o.ShippedDate
FROM @TempItems t
INNER JOIN Orders o ON o.OrderID = t.OrderID
INNER JOIN Customers c ON c.CustomerID = o.CustomerID
INNER JOIN Employees e ON e.EmployeeID = o.EmployeeID
WHERE
t.[ID] >= @startRowIndex
AND
(o.OrderID LIKE @intOrderID OR @intOrderID = '')
AND
(o.CustomerID = @strCustomerID OR @strCustomerID='')
AND
(o.EmployeeID = @intEmployeeID OR @intEmployeeID = 0)
AND
(o.OrderDate = @dteOrderDate OR @dteOrderDate IS NULL)
SET ROWCOUNT 0
GO






when i execute the sp with @sortOrder = 0, it works fine
exec CustomPaging '','',0,null, 1, 10, 0

but if i try anything else (@SortOrder=1) i get the error message
exec CustomPaging '','',0,null, 1, 10, 1
Syntax error converting datetime from character string.

but im unsure what is causing this problem? and how to sort it?

Any help is greatly appreciated.

Cheers.
Craig