Object reference not set to an instance of an object.

I have an asp.net app that I am trying to amend and have got stuck with the following error that comes up immediately I try to run it. Any suggestions about how I might identify the cause of the problem?
Clive Richardson
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Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
ConfigurationVB.WebForm1.Page_Load(Object sender, EventArgs e) +78
System.Web.UI.Control.OnLoad(EventArgs e) +67
System.Web.UI.Control.LoadRecursive() +35
System.Web.UI.Page.ProcessRequestMain() +744

We need to see the code that runs when the page loads.
Zath
Sorry... I found the problem. To do with a class that reads web.config.
Clive R