I converted my web application from .NET 3.5 to .NET 4.0 and ported it to IIS 7.0. All of a sudden the AutoComplete Extender stopped working.

After some research I found that my web.config file needed the followings:

<system.webServer>

<handlers>

<add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>

<add name="ScriptResource" verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>

</handlers>

</system.webServer>

I added these handlers and the AutoComplete Extneder was back to work.

Hope this may help others to solve the similar problems.

Happy coding to everyone !!