Lync Server Web Conferencing Server failed to load the external proxies list. Failed to connect external users because the ...

Lync Server Web Conferencing Server failed to load the external proxies list.

Failed to connect external users because the list of proxies is empty. 
Failure occurrences: %1, since %2.
Cause: Empty or invalid topology settings for edge services.
Resolution:
Check your edge services topology entry for errors.