Error with Using XMLHttpRequest and jQuery AJAX to implement a cascading dropdown

I tried to look into the problem and it seems the reason for the problem is:

When the page loads it has some values associated with the controls and asp.net knows about them (viewstate perhaps). Now we change the values on client side and them make a postback. this will make the asp.net to validate the values with the old values it knows about and they will not match. This will make it think that the some script is being injected.

Now this behavior is by default. To circumvent this problem, we can either use the AJAX mechanism that will update the values that asp.net knows along with the values on client side. This can be done by using the ASP.NET ajax framework to implement the cascading dropdows i.e. using Updatepanel.

Or we can turn of the event validation for the page having the xmlhttprequest code i.e. enableEventValidation="false"

Now this will open up the page for potential hacks in form of XSS but one should not solely rely on this eventvalidation to avoid XSS anyways. We need to have strong server side validations to check all the user input. Event validation is not always necessary if you our code does not use the values sent from the user. As long as we have strong server side validations put in place the event validations can be turned off(although not recommended.

I first appreciate your prompt and kind attention to my question and tweets.
Now instead of using this way Ajax, as a friend of mine suggested, I used jQuerry Ajax that inside it, updating Asp.net is done automatically. But since I like to know what and how is something done, I would insist that there must be a way to overcome this error not by turning of page validation. If jQuerry is doing it, we must be able to do it, too. MS has issued some code but those are server side too I have commented it, hope to receive reply. Yet I keep this open for others to give their reply.
Thanks
aebrs@yahoo.com