Wac discovery has failed on server {0}. Please check the Owa web.config on this exchange server for BlockWacViewingThroughUI ...

Wac discovery has failed on server {0}. Please check the Owa web.config on this exchange server for BlockWacViewingThroughUI app setting. It should not be set to true. Also please manually hit the Wac Discovery Url configured under WacUrlHostName in owa web.config and see if it is returning a valid xml with external-https net zone. If not, please contact wac team (wac911) regarding the same. If yes, please debug why our exchange server is not able to hit this Url and parse the external-https net zone.