Please help me to resolve my ajax error

i am using asp.net (.net framework 2.0) i am getting below error for my ajax popup extender

error :

 Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled.

Details: Error parsing near 'The server rejected '.

actually is not giving me error on localhost, i have uploaded it开发者_如何学编程 on 2 other different server on 1 server its working fine but on other server its giving me above error. (on server where is working fine has got windows 2000 and on which its giving error its ms windows 2003). this is link where its giving me error : highschoolers its on "Join new for free" button ..

I checked the AJAX response and found what is probably the real error:

The server rejected the sender address. The server response was: 501 Your domain does not seem to be valid. Could not find MX record for your domain.

Take a look at the code you're using e-mail out.