Return Stored Procedure Parameter

I'm attempting to return a value from my stored procedure. Here is my button click event that runs the stored procedure. protected void btn_Move_Click(object sender, EventArgs e)
{
/*variables need for the update of the old staff record
and the creation of the new staff record.
*/
BMSUser bmsUser = (BMSUser)Session["bmsUser"];
int staffid = Convert.ToInt32(bmsUser.CmsStaffID);
int oldStaffProfileID = Convert.ToInt32(Request.QueryString["profileid"]);
string newManager = Convert.ToString(RadComboBox_MangersbyOrg.Text);
int newMangerProfileID = Convert.ToInt32(RadComboBox_MangersbyOrg.Value);


SqlConnection conn = new SqlConnection(connect);
SqlCommand cmd = new SqlCommand();
cmd.Connection = conn;
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "sp_BMS_MoveStaffMember";
cmd.Parameters.Add("@OldStaffProfileID", SqlDbType.Int);
cmd.Parameters["@OldStaffProfileID"].Precision = 9;
cmd.Parameters["@OldStaffProfileID"].Scale = 0;
cmd.Parameters["@OldStaffProfileID"].Value = oldStaffProfileID;
cmd.Parameters.Add("@NewManagerProfileID", SqlDbType.Int);
cmd.Parameters["@NewManagerProfileID"].Precision = 9;
cmd.Parameters["@NewManagerProfileID"].Scale = 0;
cmd.Parameters["@NewManagerProfileID"].Value = newMangerProfileID;
cmd.Parameters.Add("@LastModifiedBy", SqlDbType.Int);
cmd.Parameters["@LastModifiedBy"].Precision = 9;
cmd.Parameters["@LastModifiedBy"].Scale = 0;
cmd.Parameters["@LastModifiedBy"].Value = staffid;

SqlParameter sp = new SqlParameter("@OLDManagerReturn", SqlDbType.Int);
sp.Direction = ParameterDirection.Output;
cmd.Parameters.Add(sp);

lbl_ERROR.Text = Convert.ToString(sp);

conn.Open();
SqlTransaction trans = conn.BeginTransaction();
cmd.Transaction = trans;
cmd.ExecuteNonQuery();
conn.Close();

 My parameter sp is coming back null for some reason. Am I not setting the parameter correctly? I set a break point and it says the value is null.

 Here is the parts of my stored proc returning the value...


DECLARE @OLDManagerReturn numeric(9)

SELECT @OLDManagerReturn =  ManagerProfileID FROM tblBMS_Staff_rel_Staff WHERE StaffProfileID = @OldStaffProfileID AND Active=1 AND BudgetYear = @BudgetYear

RETURN @OLDManagerReturn