Please check if the DAPNET server is working. Sometime it gets unreachable for hours. You can also take a look at the openSPOT2 log on the status page to find out what's happening.
Also take a look at this:
https://hampager.de/dokuwiki/doku.php?id=blog:connection_problems_solved
If you are blocked, you can unblock yourself here:
https://hampager.de/blocked-ips/
Also make sure you use your correct transmitter callsign and password, but the OS2 will display a warning if the server won't let you connect because of invalid credentials.