Here's another nice, simple way to pass values from one page to another:
(VB.NET code)
'Add data to the context object before transferring
Context.Items("myParameter") = x
Server.Transfer("handle_error.aspx ")
Then, in handle_error.aspx.aspx:
'Grab data from the context property
Dim x as Integer = CType(Context.Items("myParameter"),Integer)
Of course there are a number of ways to pass values from one page to another
besides the querystring there are cookies, session, context, saving to a
temporary table in the database between each page, etc.
You'll have to decide which technique is best for your application.
Here are more good articles on the subject:
http://SteveOrr.net/faq/PassValues.aspx
http://www.aspalliance.com/kenc/passval.aspx
http://msdn.microsoft.com/msdnmag/issues/03/04/ASPNETUserState/default.aspx