Document.getElementById(update[0]) is null

Answer 1

Edit, for updated question: Your site appears to work for me now, be sure to clear your cache with Ctrl+F5 if you're still having issues.

Your if() check is a little off, this:

if(response.indexOf('|' != -1)) {

should be:

if(response.indexOf('|') != -1) {

currently you're getting a false positive, and the code inside that if shouldn't even be executing...but they are :)

Answer 2

What's the value of update right before your getElementById line? Use console.log or equivalent to see if the array includes what you expect.

Answer 3

This means that whatever you're returning in the responseText, is not what you're wanting.

If you're returning

"updatePanel|my message"

you need something on your page like this:

<div id="updatePanel">your message will go here</div>

So check your return value by alerting or inspecting the responseText. Firebug will help you.