I checked the Windows Phone Community on the Microsoft website and came across an old solution, but one that still might work for you.
Wordament requires a connection to your Xbox Live account. By powering off your phone, then powering it on again, you force Xbox to re-establish that connection (basically, you're logging off/logging on xbox live).
I opened Wordament on my WP to verify that the service is up. I'm in 1181st place out of 1180 players currently online.
Please reply if this resolves your problem. Others might find the fix useful also. And I encourage you to become a registered member of the WPC community!