I have been working on this for nearly 24 hours and still have not been able to discover the solution.  I am turning to the knowledge in the SF collective to see if anyone has run into something like this before.

Something changed on our IIS yesterday that brought everything to a screeching halt.  One of the main errors that I received was this one:

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.

I added the tag to the web.config file (as the error suggests) knowing that this is an intranet application and I am comfortable doing this...the app began working again; however, not everything works.  Most pages will not run local scripts.  Some pages do not run server scripts (from postbacks).  I am completely baffled as to what is going on.  I recreated the virtual folder...I even moved the entire app to another server...the same thing is happening.

I am really hoping someone here can shed some light on this.  Some of our critical systems are involved.  Many are breathing heavily down my neck ready to pounce on me.

Thanks!
Bill