Invalid postback or callback argument.

I was tring to move some web apps to a demo server and ran into this error message on one of them.

Invalid postback or callback argument. Event validation is enabled using in configuration or <%@ Page EnableEventValidation="true" %>in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.

what made this move interesting is that the page is a aspx page that was converted from a asp page some time ago and that it was still configured as a dot net 1.1 app in iis. When I moved it, i saw the aspx ending and set it us as a dot net 2.0 app. Changing it back fixed my issus.

I did find this link to a related issue and would have tried those steps if my trick did not work.
http://www.netnewsgroups.net/group/microsoft.public.dotnet.framework.aspnet/topic637.aspx