ASP.NET trapping variable for error message

Given the following code on an error trapping page:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Master.Header = "Web Site Error"
        lblErrPage.Text = "Error on Page: " & Request.QueryString("aspxerrorpath").ToString
End Sub
If we need to know what causes the error. what would be the ASP.NET trapping variable for the error message as "aspxerrorpath" is for the culprit page name?
Thanks
 
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