OWA is currently unable to handle this request HTTP ERROR 503

Our client called and mentioned that some of thier users cannot access to Outlook Web Access (OWA) with the following error message

mail.aventislab.com is currently unable to handle this request HTTP ERROR 503

The following error message shown in Microsoft Remote Connectivity Analyzer for Microsoft Exchange Web Services Connectivity Tests

It seem like the error message is related to AutoDiscover in Exchange 2013 Server, and we manage to resolve this issue by following the steps below

1. Our client had recently purchased a Wildcard SSL Certificate and install it in thier Exchange 2013 Server

2. We noticed that the SSL Certificate is NOT binded to Exchange Back End – https (441)

3. Binded the Wildcard SSL Certificate to it, and users can login to thier OWA now