Any way to verify that this has been installed on the server? I'm running 3.5 .NET Framework.
Asp.Net Ajax extensions are part of the 3.5 framework, so they should be installed. They live in the System.Web.Extensions
assembly.
You can verify that that .dll exists by checking your GAC. The .dll's also physically live in the Windows\Microsoft.Net\assembly\GAC_MSIL directory, which you can see with explorer on Windows 7 but will be hidden in XP (use a command line to browse to the directory).
Check this out - Talks about http://msdn.microsoft.com/en-us/library/bb907614.aspx
This topic describes two tasks:
How to use reflection to check for the System.Web.Extensions assembly. This check is useful when you create custom controls that work regardless of whether ASP.NET AJAX is installed.
How to use the GetCurrent method of the ScriptManager class to determine whether AJAX features are enabled on an individual page. This is useful because scripts that are used in asynchronous postbacks must be registered with the ScriptManager control. Otherwise, the scripts can be registered with the ClientScriptManager control.