I'm unable to log into cmsdesk, I get this whenever I try to log into the site.

viewing the site from the normal page is fine, but cmsdesk won't let me in. How can I fix this?

Invalid postback or callback argument. 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.