AJAX :: How To Remove Invalid Control Characters

I used many methods but not getting the output, till yesterday it was working but cant understand now whats happening??

i enter the right data but still it returns this error:

"Invalid control characters"

see my code;

public string officelist(string uname, string pwd, long id) {
WebReference,CommonWSEndPointService eps = new
WebReference.CommonWSEndPoinService;
string url = "xxxxxxxxxxxxxxx?wsdl";
HttpWebrequest req = (HttpWebRequest)WebRequest.Create(url);
req.connection = eps.m291524(uname,pwd, id);
string conn = req.connection;
return con;
}