Error: Sys.ScriptLoadFailedException:

Maybe check that all references to javascript in the HTML source return valid javascript.

It also may be that one of the scripts isn't registering properly.

I think you may need to register at the bottom of your custom javascript files (if you have any)

that the script has loaded.

Like this:

if( Sys && Sys.Application ){
Sys.Application.notifyScriptLoaded();
}

Sounds like your AJAX environment isn't setup correctly. There are some things to check that may help:http://blogs.visoftinc.com/archive/2007/09/23/asp.net-ajax--updatepanel-not-working--common-problems.aspx

-Damien