Same version of .Net framework is my first question? Also, why on earth are you trying to make a request to a url with forward slashes after the file name???? Use query parameters, that's what they are there for! You're url may well be seen by VS2003 as invalid and so return an error page. Your URL should be Default.aspx?Method=GetDateVal and in your code behind do something like
if(Request["Method"] == "GetDateVal")
Response.ContentType = "text";
It looks like this is just an example of jQuery ajax methods - you should certainly never get the time from the server in a practical application. Two reasons: 1 time zones and time differences between both your user and your own server(s) (and between one of your serevrs and another server) - always store stuff in databases for example by UTC time and then convert to local time on display. Secondly: It would put a huge unnecessary load on your server!
Anyway, hope this helps, Ed
Edit: Also, seen this a lot recently, charset should NOT be defined in the content type - where ever this is coming from has got it wrong and charset has it's own header - so far as I'm aware jQuery will not split up the ContentType passed to it into these two separate headers for you.