Host not found error on second application start.

I Get/post request to a server using QNetworkAccessManager works fine for the first application start. (using GPGS/3G) . I waited one time start again the application an "Host not found" error when the request is made. I have to exit the software and then connect successfully. (but not every time)
it fails when the network icon disconnect

if(reply->error()==QNetworkReply::HostNotFoundError)
{
emit commError(&error);

}
reply->deleteLater();

how to maintain the network connection?