"The following message could not be delivered..."

Whenever I type anything on WLM today I get the message “The following message could not be delivered to all recipients.” The person I’m chatting with says he still gets my messages, but it’s pretty annoying…
This usually only happens when there’s something wrong with my internet or his internet, but we’ve both restarted, signed out and back in, turned our wi-fi off and on… Is there something wrong with the servers? Any way to fix this?