Error in app_start help needed

[Jon]

I have custom error handling configured for my application. In web.config I have:

<customErrors defaultRedirect="ErrorDisplay.aspx" mode="On">

<error statusCode="404" redirect="Error404.htm"/>

</customErrors>

This works very well, except in Global.asax. The following code throws an error in the data layer, which rethrows the error and gets caught in the try block below. I then throw my error (a custom class derived from the ssytem exception type). When I do this in any other page, it redirects to my custom error page as expected. However, in the App_Start of global.asax, it does not and the app goes on to display the first page of the site, not the error page. Is there a reason for this, am I doing something wrong? Thanks.

Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)

' Fires when the application is started

Dim dsPriority As DataSet, oNetData As MSIData, dbCon As SqlClient.SqlConnection

Try

strDefConString = System.Configuration.ConfigurationSettings.AppSett ings("ConnectionString")

oNetData = New MSIData

dbCon = oNetData.GetConnection(strDefConString)

Application("PriorityListDS") = oNetData.SProcDataSet(dbCon, "GetPriorityList")

Catch ex As Exception

Dim excNew As MSIException = New MSIException("An error occured during application start." + ControlChars.NewLine + ex.Message)

excNew.TrueSource = "Application_Start"

Throw excNew

End Try

End Sub