Web application and 'The page cannot be found' page?

[Guest]

I have a user that starts entering data into the web application (it's all in
a Wizard control) and every once in a while when she jumps from one page to
another she gets the 'The page cannot be found' Internet Explorer page. She
refreshes the page and everything works fine. In my testing I never got this
page.
Is there any way I can avoid this?
I have VS 2005 v2.0

Thanks.