Question: <http://technet.microsoft.com/en-us/library/jj219455(v=office.15).aspx>
We have followed the TechNet article carefully and we have been successful, however, Office documents do not open in OWA.

I get the error "sorry we couldn't open this presentation because we run into a problem, please try again", same with Word, slightly different with Excel.

Our server names are set as External-https. Our SP configuration part has been exactly like described by the TechNet article. The binding is successful (and it does say external-https) and the SPWOPI has been changed to external-https.

We run out of ideas. Can anybody help?

Answer: 
This behavior could be caused if you have your Alternative Access Mapping (AAM) Default Zone set to use protocol http while your OWA is set to use HTTPS. One solution I found is to change the Default Zone to use HTTPS.

Change the Default Zone by going to `Central Administration > Application Management > Configure Alternative Access Mapping > MyWebApp > Edit Internal URLs` and set protocol to HTTPS.

![enter image description here](https://i.stack.imgur.com/RKsGk.png)

Reference: [SharePoint 2013 Office Web Apps Problem - Unable to Open/View/Edit](http://social.technet.microsoft.com/Forums/sharepoint/en-US/f7be5f88-8c98-464e-8596-60956b5e98fd/sharepoint-2013-office-web-apps-problem-unable-to-openviewedit?forum=sharepointgeneral)
Before few days I was having same issue. Office web app was install correctly and every thing was done correctly. But still when I was trying preview any file I was getting error "**Sorry we couldn't open this ...**"

Then I start digging ULS logs and I found SPWOPI is failing due to net tcp. So I did steps as below 

1. My first step was go on the both the server's services and check net tcp is running or not. But I found net tcp service was missing.
2. Then I go to Windows features and Install HTTP activation and Non-HTTP activation. You can add both for .Net 3.5.1 and 4.0

You can follow this <http://rohitguptablog.wordpress.com/tag/net-tcp/> 

Hope this can help you to solve the issue