The remote server returned an error: (400) Bad Request.

Any one Helep Me I am using contractcontact.com api Problam is that whenever I select 30 records it works properlly but select 35 record then get
The remote server returned an error: (400) Bad Request
my code is following

byte[] byteArray = Encoding.UTF8.GetBytes(postData);
// Set the ContentType property of the WebRequest.
request.ContentType = "application/atom+xml";
// Set the ContentLength property of the WebRequest.
request.ContentLength = byteArray.Length;
// Get the request stream.
Stream dataStream;
try
{
dataStream = request.GetRequestStream();
// Write the data to the request stream.
dataStream.Write(byteArray, 0, byteArray.Length);
// Close the Stream object.
dataStream.Close();
}
catch (WebException exWrite)
{
throw exWrite;
}
catch (Exception genException)
{
throw genException;
}
// Get the response.
WebResponse response=null ;
try
{
response = request.GetResponse();
// Display the status.
Console.WriteLine(((HttpWebResponse)response).StatusDescription);
}
catch (WebException exResponse)
{
throw exResponse;
}
StreamReader reader;
try
{
// Get the stream containing content returned by the server.
dataStream = response.GetResponseStream();

// Open the stream using a StreamReader for easy access.
reader = new StreamReader(dataStream);
// Read the content.
}
catch (WebException exWrite)
{
throw exWrite;
}
catch (Exception genException)
{
throw genException;
}
string responseFromServer = reader.ReadToEnd();
// Display the content.
Response.Write(responseFromServer);
// Clean up the streams.
reader.Close();
dataStream.Close();
response.Close();
_msg.erorrMsg = "mail has been successfully sent";
_msg.erorrType = "1";

}
catch
{ _msg.erorrMsg = "Sorry! unable to send mail.";
_msg.erorrType = "2";

}