*** UPDATE ***
This issue has been resolved in the WAC November 2013 update: http://support.microsoft.com/kb/2837634/en-us.
Remember that in order to install this update you must first remove the existing farm, install the update and then recreate the farm. See this article if you need a reminder.
Did some maintenance last weekend, installing the October 2013 update and other updates.
additionally, Had my work station upgraded to Windows 8.1.
The first thing I noticed was that PowerPoint presentations content is unavailable after installing the updates, with the following error:
“Sorry, we ran into a problem displaying the presentation. Please try again.”
After testing this on multiple machines with multiple accounts, I can verify that Lync 2013 clients on Windows 8.1, are unable to present or view PowerPoint content on Office Web Apps Server.
This goes for Office Web Apps Servers installed on Windows Server 2008R2, Windows Server 2012 and Windows Server 2012R2, both internally and externally.
Lync 2013 clients on any Operating system OTHER than Windows 8.1 are not affected and can use the Office Web Apps services with no issues.
Keep that in mind before upgrading to Windows 8.1!