The reason behind this error definitely makes it into my top 10 of mistakes! I'm still not sure who's mistake it was, mine or Microsoft's, but I'm assuming that it's mine to be on the safe side.
The error message "PowerPoint Web App encountered an error. Please try again." doesn't really tell you where to look, but it's quite clear that you should start at the web application and check if it's operating properly. My problem was that the PowerPoint Service Application actually was a Word Viewing Service Application. It's easy enough to fix by deleting it and recreating it, however here are some other approaches that you might find useful.
- Open the Central Administration
- Go to Application Management and select Manage service applications in the Service Applications section
Locate the PowerPoint Service Application
- If you have one that is actually a PowerPoint Service Application, remove it an recreate it
- If you can't find one, create it.
- Go back to the Application Management page and select Configure service application associations
- Make sure that the Web application that you're getting the error on has a PowerPoint Service Application Proxy in its Application Proxy Group
- Go back to the Application Management page and select Manage services on server
- Make sure that there's a PowerPoint Service with the status Started on the server that you're getting the error on
If it's still not fixed, you can comment below and I'll get back to you with the solution as soon as possible!