[jQuery] $ajax() problem

[yi]

$.ajax({

                                        type: "POST",

                                        url: "mywebpage.aspx?Arg="+args2,

                                        contentType: "text",

                                        data:"{}",

                                        dataType: "text",

                                        success: CompleteInsert,

                                        error: onFail

                                });

I dont know why the onFail function is going to be executed when args2
is too big.
args2 is a string type
can anyone explain this
thanks