Office 2013 Retail deactivating itself

I have a strange problem where Office is deactivating itself, but only for a small number of users.
I'm absolutely sure their keys are only used once.
Did you see anything like this ?
I get two messages:
Microsoft Office cannot verify the license for this product. You should repair the Office program by using Control Panel.


We're sorry. but Word has run into an error that is preventing it from working correctly. Word will need to be closed as a result. Would you like to repair now.

My PCs have limited access to the internet, and they are going on-line through the proxy, but the installation (and activation) was done with internet fully opened / without proxy.

Nothing worked so far. I cannot repair, activate over internet or phone.

I even uninstalled it and reinstalled with completely new, still sealed key, and it happened again after few days.

What is strange is that the reboot will fix it for few days, and then, it will happen again.
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

*** Hopeleonie ***IT ManagerCommented:
You must remove all traces of the Office installation by downloading the fixit from the following article:

After reinstall Office by logging into with your registered email address and click Install Office.
tp-it-teamAuthor Commented:
OK, I found the problem - Trend Office AV.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
tp-it-teamAuthor Commented:
No one was able to help me and I found the exact reason for my problem.
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Microsoft Office

From novice to tech pro — start learning today.