Accessing a CheckBoxField

[dwg1011]

I have a detailview with several fields ending with the CheckBoxField shown
below:

<asp:CheckBoxField DataField="aruExtraFields"
HeaderText="Extra Fields?"
ReadOnly="false"
SortExpression="aruExtraFields" />
</Fields>
</asp:DetailsView>

Please note the asp control is NOT part of a template.

In the code behind in the AlertRulesDetail_ItemUpdated, I am trying to
access the value of the field using the code:

Dim CheckBoxName As CheckBox
CheckBoxName =
CType(AlertRulesDetailView.FindControl("aruExtraFi elds"), CheckBox)

Unfortunately, the FindControl does not return anything. I have also tried
declaring the CheckBoxName field as CheckBoxField and changing the type in
the FindControl, but that doesn't work either.

Can somebody please tell me what I am doing wrong.

Thanks,
David