Web Forms :: Maintain Ddl Values When Page Changes From Default To History?

i have a master page that has a an accordion and inside the accordion is a cscading dropdownlist and then a button... Basically you select the values from the dropdowns and the click the button to change the content form from default.aspx to history.aspx. This works fine the first time I do it with the exception that cascadiing ddl all reset and then if i populate again and clcik the button again I get the following error(below)... I know I can set enableEventValidation = false, but wondered why this is occuring and what effect setting it to false would have? The second part of the question would be how do I maintain the ddl values when the page changes from default to History.sapx? I am using the following for the button.

<asp:Button ID="btnNewRecord" runat="server" Text="New" PostBackUrl ="~/History.aspx" />
Event validation is enabled using <pages enableEventValidation="true"/> 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.