Forms Data Controls :: Use A Query String Variable Created On The Fly To Populate A Child Webpage?

I have developed the below web page which has an asp.net 3.5 listview control as it's frontend and an sql server db as it's backend.

[URL]

The first row on the web page is the inserting row. What I am hoping to achieve is that when the user enters their appropriate data they click the "Next" button to assign this dataset with it's own identity ID (customer_id) value within my database (this works perfectly), at the same time on the fly I want to use this customer_id as a query string variable to populate a child page (customerTrades.aspx) in order to pin further data to this identity. Currently I am attempting to use the below code within the iteminserted event of my listview control but I receive the error: "object reference not set to the instance of an object"??

protected void lvTrustAccounts_ItemInserted(object sender,
ListViewInsertedEventArgs e)
{
string customerID = e.Values["customer_id"].ToString();
Response.Redirect("http://www.tradeselector.co.uk/customerTrades.aspx?customer_id="
+ customerID + "");
}

Is this because the child page cannot find the customer_id variable being passed through the query string? Because it's not actually created yet? Am I using the wrong listview event? How can I achieve what I am looking for?

I must also mention that I'm using a linqdatasource to insert my data on runtime into my database. However, I am using the listview iteminserting event to insert my frontend dropdownlist selected values, code below:

protected void lvTrustAccounts_ItemInserting(object sender,
ListViewInsertEventArgs e)
{
e.Values["customer_created_date"]
= DateTime.Now;
e.Values["customer_update_date"]
= null;
DropDownList ddl_CountyInsert =
(DropDownList)lvTrustAccounts.InsertItem.FindControl("CountyInsertDDL");
DropDownList ddl_CityInsert =
(DropDownList)lvTrustAccounts.InsertItem.FindControl("CityInsertDDL");
DropDownList ddl_CountryInsert =
(DropDownList)lvTrustAccounts.InsertItem.FindControl("CountryInsertDDL");
e.Values["customer_county_code"]
= ddl_CountyInsert.SelectedValue;
e.Values["customer_city_code"]
= ddl_CityInsert.SelectedValue;
e.Values["customer_country_code"]
= ddl_CountryInsert.SelectedValue;
}