Pfthb

I have an app that uses an apache server on a remote machine.
I use HttpWebRequest method post to connect to the server.
Sometimes(rarely) on the first connection to the server (and all the subsequent ones) I get an exception.

System.Net.WebException: 'An error occurred
while sending the request. The text associated with this error code
could not be found. A connection with the server could not be
established

I try to restart apache, restart the app and it behaves the same way. Meanwhile, I use the app on that server and it works correctly there.
Now, when I restart the server PC (not apache) it works again.
What could the problem be?
It is not the server code, because it works locally at the same time, I don't think it is the firewall because it would not work even after I restart the pc (server). The only thing I can think of is some app that could prevent another pc from accessing the server.

Anyway, here is the code

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = buffer.Length;
request.CookieContainer = cookies;
Stream postData = request.GetRequestStream();
postData.Write(buffer, 0, buffer.Length);
postData.Close();

// Get and return response
HttpWebResponse response = (HttpWebResponse)request.GetResponse();