VS 2008 - MWeb App Error On DetailsView

I have a Default web page that has several text fields on it to allow users to search the SQL 2008 database. The bottom half of the default web page then loads a grid view based on the search criteria and records found in the database. The Select link is visible, which, when clicked brings the user to the next aspx screen that contains the detail view of the selected record, with the appropriate data being displayed from the database.

All continues to work fine when I click the Edit button as I am then brought into the 'Edit' view, if you will, of the details view. The issue arises when I click the Update button when trying to update the record. The same error messages are received when I try to insert a record too.

Here is the code that creates the details view and the necessary update/insert record coding. The error received is: Index (zero based) must be greater than or equal to zero and less than the size of the argument list. The error is placed on line 76 which is:

Code:
Dim txtSerialNumber As TextBox = CType(myDetailsView.FindControl("txtEditSerialNumber"), TextBox)

Code:
<asp:DetailsView ID="myDetailsView" runat="server" AutoGenerateRows="false" >
<Fields>
<asp:TemplateField HeaderText="Serial Number">
<ItemTemplate>

[code]..