Am a keen follower of Microsoft's SharePoint Blog and proud to provide this direct from the Microsoft Tech Community:

Problem: You receive a “Sorry, this document can’t be opened for editing” error when you try to create or edit an Office document in Office Web Apps.

 

Issue 1:

In some situations, users that are members of Active Directory (AD) Security Groups may be unable to edit documents in the browser. The solution is to ensure the User Profile Service Application (UPA) is properly configured and fully synchronized with user and group memberships. For more information, see the KB article SharePoint 2013 Unable to edit Office Web Apps 2013 files with users that are members of security groups.

 

Issue 2:

This error will also occur if co-authoring is disabled on the web application. For more information, see the KB article Disable co-authoring in SharePoint Server. Make sure that co-authoring is enabled ($web.DisableCoauthoring = $false) on web applications using Office Web Apps.

 

 

asnp *sh*

##RUN THIS TO SEE WHAT STATE IT SET TO
$web = Get-SPWebApplication <webapplication>
$web.DisableCoauthoring

##RUN THIS TO SET CO-AUTHORING TO ENABLED
$web = Get-SPWebApplication <webapplication>
$web.DisableCoauthoring = “False”
$web.Update()

 

 

Note: Disabling co-authoring via PowerShell ($web.DisableCoauthoring = “True”) will break Office Web Apps functionality for Microsoft Word. Microsoft Word Web Application requires Co-authoring to be enabled to function properly and is enabled by default.

 

For more information see: Configure Office Web Apps for SharePoint 2013

The above is kindly provided by the Microsoft Tech Community!