Help With Dynamic SQL Stored Procedure

I have a stored procedure spGetAccessLogDynamic and when I try to call
it I get the following error:

Server: Msg 2812, Level 16, State 62, Line 1
Could not find stored procedure 'S'.

I dont know why because I dont have anything refering to stored
procedure 'S'

I have ran my SQL String with sample values and it works fine. So I
am presuming that it is some kind of syntax error in my stored
procedure but have tried everything and cant find it!

Anyway here is the sample data I am using to call it and my sp

Exec spGetAccessLogDynamic '24', '2005/07/04 00:00:00 AM', '2005/11/04
00:00:00 AM', 'TimeAccessed DESC'


CREATE PROCEDURE spGetAccessLogDynamic
(
@PinServiceID varchar (4),
@StartDate varchar(40),
@EndDate varchar(40),
@SortExp varchar (100)
)

AS

-- Create a variable @SQL Statement
DECLARE @SQLStatement varchar

-- Enter the Dynamic SQL statement into the variable @SQLStatement
SELECT @SQLStatement = ( 'SELECT A.PinValue,A.TimeAccessed,
C.Forename, C.Surname
FROM AccessLog A, Members C, Pins P
WHERE P.PinValue = A.PinValue AND
P.MemberID = C.MemberID AND A.PinServiceID= ''' + @PinServiceID + '''
AND A.TimeAccessed BETWEEN dbo.func_DateMidnightPrevious( ''' +
@StartDate + ''' ) AND dbo.func_DateMidnightNext( ''' + @EndDate
+''')
GROUP BY A.PinValue,
A.TimeAccessed, C.Forename, C.Surname
ORDER BY ' + @SortExp)

-- Execute the SQL statement
EXEC ( @SQLStatement)
GO

Any help would be very very much appreciated!!!!!!

Thanks
Caro