Thanks for your reply, but that is one of the main documents I used for setting up Office Web Apps. Its troubleshooting section is fairly sparse and while it does mention the error I'm getting, their answer is something I had already checked. I've looked in the error logs on the server and based on what I'm seeing there and the results of researching those errors, I'm coming to the conclusion that the problem is with the certificate since I'm using an https site, not http (the client wants access mainly from outside the LAN). My research indicates that the internal host domain must be in the SAN of the certificate. However that is not possible because new certificate rules state that you cannot include NetBIOS names of servers and private domain names such as domain.local in the SAN of certificates anymore. And the errors on the server certainly look to me as if the private domain name is involved.
So this seems to be an impasse and I don't know how to fix it.
Jonathan