JC, EWS is different than OWA. All because you can access OWA does not mean EWS will work for you.
I test EWS issues via a free utility called EWS Editor.
I have the same issue as JC and I tested against exchange 2007 and 2010.
I verified I can log into the mailbox through EWS.
I compared the EWS autodiscover URL against the URL Alertcentral discovered. They are identical.
Maybe Alertcentral has a SSL compatibility issue in general?
Has anyone ever successfully used EWS for AlertCentral. Can you share what you used to input for the setup? Especially how you presented the login:
Was it just the AD login
Or domain\login
or login@domain
Must be something silly, unless it is a SSL issue.