>I am using VS2005 version 2.0.50727.3082.
>
>We have a user that is getting the following error message in his IE while using our web app.

This is a security feature of ASP.NET - it's essentially checking that what the user sends back to you was originally generated on the server. You'll sometimes get this if the user clicks on something on the page before the rest of the page has rendered, which causes this check to fail (since some of the data is missing). You can also get this if you have some client-side scripting that messes with an ASP.NET control (ex. adding new values to the control dynamically on the client).

You can disable this security checking by editing the ASPX page and set "EnableEventValidation" in the Page tag to false.

<%@ Page EnableEventValidation="false"