Make sure you have a functioning Internet connection. Using the same computer, try to surf to diasend.com using your usual web browser. If this does not work, please contact your local network provider.
Even if you do have a working internet connection, there could be a firewall between your computer and the Internet. Make sure that TCP port 80 is open for outgoing TCP port 55715 will need to be open for data transmission.
Note: if you are trying to download your device from your office, school, etc and get the message “no contact with server”, then there is most likely a firewall issue and you will have to contact the IT department where you are located.