"A first chance exception"

Question

When I am debugging a C# 2010 web application, I am getting the error, "A first chance exception of type 'System.Web.HttpParseException' occurred in System.Web.dll" sometimes.

I am wondering if you can suggest in what situations this error could be occuring and/or possibly help me to determine when this type of error is occuring?

The only thing I  think that can be causing this error is when a user finishes working on my new pages on the company website. My new web pages run in a series of 5 pages. When they have finsished entering data for one customer i redirect the user to the first of the 5 pages. at any point the user can click the 'logout' button that is at the top of all the master pages. Could this be an issue?