I would edit your web.config so you can see the actual error message.  Modify the following line of your config file:

<customErrors mode="RemoteOnly">

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to this:

<customErrors mode="Off">

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Or, if you do not want to do this, logon to the server where this application lives and try to go to the URL which is giving you the error.

Please post the error full text of the error message.

Dan

Dan -

Thank-you for your help with this!

Where is the config file located? I attempted to do research (google) with no luck. I logged into IIS but I'm not sure where to go.

In regards to where the application resides, I entered the URL of the file and it still gave the same error
URL of file was http://<servername>/Shared%20Documents/test.xlsx?Web=1

Couple things to note -
When I deployed the single server office web apps server to use HTTP, I entered this line into PowerShell
New-OfficeWebAppsFarm -InternalURL "http://<servername>" -AllowHttp -EditingEnabled

When running above PowerShell command, I get a notice that says "You should only do this if users of this office web apps server have licenses that permit editing using office web apps." I went ahead and chose "Yes" even though I'm not sure what that means. Everyone has a copy of Office on their machines.

It's also worth noting that I received positive installation verification when entering the following link into a browser http://servername/hosting/discovery after I set up the webapps farm.

Here is configuration information -

Thoughts?

Dan

Thanks for assisting finding webconfig file(s).

No luck on that change however. The webconfig files on the SharePoint server had
which I then changed to
I searched the WebApps server to see if the config file there even had <customErrors mode="Off"> and it had no customErrors line.

I have rebooted both my WebApps Server and my SharePoint Server.

Any further insight?

It may be worth noting that when I now go to
http://<servername>/hosting/discovery
that I get a 404 error and the configuration verification page does not show. Augh!!!!!

Scratch that last comment please. No 404.

This helped find the path to a webconfig file. thank-you!