To Mingkai Yu,
I tried responding to your private message but it says you aren't accepting them.
One thing I did in my case was return a delimited
string representing a resultset instead of formatted html. I format the delim string on the page via JavaScript. But the result was the same so it isn't the amount of physical data that Ajax is receiving. I am still trying to figure out what is happening. I believe it to be related to the div tag in which I am posting the data from Ajax. Hope that helps and let me know if you find anything..