Office is one of the more popular (if not required) programs for many activities, so having it on a system is often quite convenient to have; however, Microsoft has had an ongoing licensing restriction with its latest Office versions that prevents you from activating a previously used serial number on newer systems, even if you have uninstalled the software from prior systems. This setup obviously frustrates those who need to purchase new computers; however, recently Microsoft has changed this policy to now allow people to transfer their licenses without restrictions.
Even though this news pertains primarily to Office 2013, MacTech is reporting that the changes also affect the licensing for Office 2011 for Mac, so if you run into problems activating licenses on new systems that you have previously activated on other systems, then you will now be able to do so. However, you must first uninstall the license from the original computer before you can successfully install it on a new system.
This change comes from community feedback Microsoft received following a blog posting about its license transferability restrictions for Office 2013 and Office 365.