Hi All :
When you install Office Web Apps Server 2013 SP1 on Windows Server 2012 R2, and standalone to use OWA without Exchange, Lync and SharePoint.
You may encounter this error when you open the file:
When you look at the Event Log, you can see the Error Event ID 8115, from Office Web Apps, the general information is Could not contact WOPI End Point. Error details - 'NotImplemented url - https://XXXXX . ....'
To resolve this error, you may install Microsoft .NET Framework 4.5.2.
You can download it from this link : http://www.microsoft.com/en-us/download/details.aspx?id=42643
More information, please refer KB2901954 : http://support.microsoft.com/kb/2901954