Thanks for the quick reply.
I am using AjaxPro for ASP.Net 2.0. The application was working fine in IIS, but totally not working in apache (both asynchronous, and synchronous), and works in Cassini with synchronous only. I will revert back to the asynchronous application and test it again. If the core js file is not found, how do i determine whether is ajaxpro responsible or cassini responsible?