From time to time, Outlook may choose to disable add-ins if they take too long to open or cause Outlook to crash. This can be frustrating but it is thankfully not difficult to get the add-in working again.
1) Go into Outlook and choose File > Options
2) Go to add-ins and check which menu the add-in you are looking for is under, it will either be under Inactive or Disabled add-ins depending on what happened.
3) If it is Disabled, choose Disabled Items under the Manage menu, and click Enable to re-enable it.
4) If it is Inactive, or you have just re-enabled it from the Disabled Items menu, choose COM add-ins and tick the add-in.
5) This should allow the add-in to reload, but you may need to restart Outlook to get the functionality back.