You have Windows 10 version 1607 (Anniversary Edition) installed.
Special folders (for example, Documents or Favorites) are redirected to a file share.
User data in the redirected folders is cached locally through the Offline Files feature.
Windows Information Protection (also known as Enterprise Data Protection) is enabled on the system.
You’re using an application that's managed by Windows Information Protection.
If you try to open a file while working offline in this scenario, the attempt fails. The error message that's displayed in this situation varies, depending on the application. Word and Excel fail with the following error:
Sorry, we couldn't open '\\severname\fileshare\filename'
This issue occurs because the Offline Files feature does not support Windows Information Protection.
To work around this issue, use one of the following methods:
Open the file by using an application that's not managed by Windows Information Protection.
Open the file while you're working online (connected to your corporate network).
There are no plans to update Offline Files to support Windows Information Protection. We recommend that you migrate to a modern file sync solution such as Work Folders or OneDrive for Business.
For information about how to migrate from Offline Files to Work Folders see the following TechNet site: