Your Out of Office settings cannot be displayed, because the server is currently unavailable. Try again later.
This is perhaps the most useless error message ever invented...
To get some more information on this, from your Outlook client, press CTRL and right click on the outlook notification icon. Choose "Test Autoconfiguration".
Fill in your email address and password and click Test. This will list the various URLs that your client is using to talk to your server. The OOF URLs are the ones associated with the out of office assistant.
If you are using Outlook Anywhere, then the external URL is important. Otherwise, it is the internal URL that is important.
First verify that autoconfiguration is set properly and that your certificate is set with the correct names.
Now check the URLs being presented for out of office - in powershell this is done by :
get-webservicesvirtualdirectory -server server-name | fl *url
Where you replace server-name with the name of your server. This will list all of the URLs.
You can then set the external URL with :
get-webservicesvirtualdirectory -server server-name | set-webservicesvirtualdirectory -ExternalUrl https://mail.server-name.com/EWS/Exchange.asmx
Again replacing server-name and the URL with the correct entries.
The same can be done for the internal URL using the -InternalUrl switch.