I've the following method pulling information from a table;
public Customer GetCustomerDetails(int customerID)
    {
        Customer currentCustomer = null;
        try
        {
            using (cxn = new SqlConnection(this.ConnectionString))
            {
                using (cmd = new SqlCommand("spGetCustomerInformation", cxn))
                {
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.Add("@CustomerID", SqlDbType.Int).Value = customerID;
                    cxn.Open();
                    SqlDataReader dataReader = cmd.ExecuteReader();
                    currentCustomer = new Customer();
                    currentCustomer.CustomerID = customerID;
                    while (dataReader.Read())
                    {
                        currentCustomer.FirstName = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.firstName)).ToString();
                        currentCustomer.Surname = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.surname)).ToString();
                        currentCustomer.Email = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.email)).ToString();
                        currentCustomer.Phone = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.phone)).ToString();
                        currentCustomer.AddressLine1 = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.addressLine1)).ToString();
                        currentCustomer.AddressLine2 = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.addressLine2)).ToString();
                        currentCustomer.City = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.city)).ToString();
                        currentCustomer.County = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.county)).ToString();
                    }
                    dataReader.Close();
                    cxn.Close();
                }
            }
        }
        catch (SqlException)
        {
            throw;
        }
        return currentCustomer;
    }
However I keep getting the error "An unhandled exception of type 'System.IndexOutOfRangeException' occurred in System.Data.dll
Additional information: Index was outside the bounds of the array." on the last line in the while loop.
My SQL query looks like this:
ALTER PROC [dbo].[spGetCustomerInformation]
@CustomerID INTEGER
AS 
BEGIN
SET NOCOUNT ON
SELECT
a.Firstname,
a.Surname,
a.Email,
a.Phone,
a.AddressLine1,
a.AddressLine2,
a.City,
County
FROM 
tblCustomers a
WHERE
a.CustomerID = @CustomerID
END