File Corruption During Sync Windows 8.1

Question

Hi
I have recently introduced some Windows 8.1 systems into our environment, a Sony laptop and a non branded custom build, both systems are running Windows 8.1 Pro.
Our environment is as follows:
Windows Server 2008 domain
PPTP VPN for laptop users using a Watchguard X515.
Netgear ReadyNAS 2100 for Network Folders.
Folder redirection in place for Documents and Desktop.
Offline files in use. Users have the ability to make shared network files available offline if required.
The first device we had with 8.1 Pro was a Sony laptop for our Marketing Director.  He has manually made a few shared network folders available offline for when he is out of the office and unable to connect to the VPN.  
We first noticed an issue a few weeks ago when he came to me telling me that one of his documents were corrupt.  The file was one of the ones he has made available offline.  When he got into the office he ran a manual sync, to put the updates onto
our shared drive.  When he next came to open it, the file was corrupt with the following message:
'Excel cannot open the file 'XXXX XXXX.xlsx' because the file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file'.
I ran the file through Excel's file repair, which couldn't fix the problem and I tried a few software packages from the internet which said the file was unrecoverable, to no avail.  We tried to recreate the issue but couldn't so we put it down to a one
off.  A few days later, it happened again under the same circumstances.
I put it down to something happening while the laptop was offline, however whilst researching this, the same problem happened on a Windows 8.1 Pro Desktop.  This system never leaves the office, which led to some confusion.
Everywhere I look points to ransomware, however I have run full scans with Sophos and Malwarebytes, and both come back clean, and the issue is only occurring on 8.1 Pro systems, 7 Pro and 8 Pro systems are fine.
The user with the 8.1 Pro desktop created a test spreadsheet for me, and this morning we managed to recreate the problem.  When running a manual sync, the Offline Files comes back with an error, stating that the network copy has been deleted, would you
like to copy the local copy or delete it?  When we copy the local copy to the network, and then try to open it, we get the previous error about file corruption.
Any help would be greatly appreciated as I will have to roll the systems back to Windows 7 if I cant get it resolved, which would be a shame as the laptop is has a flip screen to turn it into a tablet.
Cheers
Jim

Answer 1

Hi,
You can boot the problematic system with clean boot to check if there is any third party software conflicts.
Steps to clean boot: 
1. Click Start->Run...-> type msconfig and press Enter
2. Click Services tab and select Hide All Microsoft Services and Disable All third party Services.
3. Click Startup tab and Disable All startup items
4. Click OK and choose Restart
5. After reboot, check whether the problem still occurs
In additional, please refer to the thread below to troubleshoot the issue:
ms excel problem
http://social.technet.microsoft.com/Forums/office/en-US/fc38d024-c767-4b9d-9ba8-60422240f579/ms-excel-problem?forum=officesetupdeployprevious
Regards,
Mandy
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