Retrieving Data Using A Stored Procedure

I have created the following stored procedure and tried to retrieve it's output value in C#, however I am getting exceptions. Can anyone tell me what I am doing wrong? Thanks!
 
 1 ALTER PROCEDURE [dbo].[GetCustomerById]
2
3 @CustId NCHAR(5),
4 @CustomerName NVARCHAR(50) OUTPUT
5
6 AS
7 BEGIN
8
9 SELECT @CustomerName = ContactName
10 FROM Customers
11 WHERE CustomerId = @CustId
12
13 END
14
15 RETURN
16
17
18
19
20
21
22 SqlConnection conn = GetConnection(); //retrieves a new SqlConnection
23 SqlCommand cmd = new SqlCommand();
24 cmd.Connection = conn;
25 cmd.CommandType = CommandType.StoredProcedure;
26 cmd.CommandText = "GetCustomerById";
27
28 SqlParameter paramCustId = new SqlParameter();
29 paramCustId.ParameterName = "@CustId";
30 paramCustId.SqlDbType = SqlDbType.NChar;
31 paramCustId.Direction = ParameterDirection.Input;
32 paramCustId.Value = "ALFKI";
33
34 SqlParameter paramCustomerName = new SqlParameter();
35 paramCustomerName.ParameterName = "@CustomerName";
36 paramCustomerName.SqlDbType = SqlDbType.NVarChar;
37 paramCustomerName.Direction = ParameterDirection.Output;
38
39 cmd.Parameters.Add(paramReturn);
40 cmd.Parameters.Add(paramCustId);
41 cmd.Parameters.Add(paramCustomerName);
42
43 conn.Open();
44 SqlDataReader reader = cmd.ExecuteReader();
45
46 string custName = cmd.Parameters["@CustomerName"].Value.ToString();