Exchange patch levels are very critical in an environment that has front-end OWA servers. The most important concept you need to realize is that the front-end servers are a proxy server to the Exchange back-end servers when using OWA. So when introducing a new Exchange server into an Exchange organization with front-end OWA servers there is a chance that the Exchange patch levels will be out of sync and OWA will fail with a "Loading" message for any user on the new Exchange server. We ran into this challenge first at a large financial services customer. Our take on it was we couldn't update all the front-end servers in a timely manner to match the new back-end server that was introduced. So we applied the workaround and waited for the next maintenance window to apply the proper exchange patches to the front-end servers. To apply the workaround for this issue review the following: