The Ghost Recon Online servers are currently down for maintenance. They are expected to come back up sometime in June.
If you are having issues connecting to the Ghost Recon: Future Soldier multiplayer servers, please visit the appropriate forum here.
Some unofficial dates that we've seen are from the Frag Dolls who advertised a "Devs and Dolls" event for Ghost Recon Online on June 15th or 16th. On top of that, the most recent contest (Avatar Contest), ends on the 14th of June. It's very possible that we'll see Ghost Recon Online back online on the 15th or 18th of June but this isn't official.
Try again after the servers come up! Check the forums daily, as there will be an announcement letting us know when that happens!