Hi,

Do you mind sharing us the whole error message that the two units were pop-up? From your description, I recommend you connect the Microsoft Customer Service Center  http://support.microsoft.com/gp/customer-service-phone-numbers/en-us and check the activation status of the two licenses. And then, you can re-activate it by phone.

Hope it's helpful.

Regards,

George Zhao
TechNet Community Support

I have installed Office 2013 on 18 units and bought licenses with each unit. After installed office, MS Office activated successfully. Out of 18, two units every day its given error that office need to be activate and when I try the same key in which I activate office it does not work and have to restart the unit and then it shows Office is activated. Any solution?