Outlook Add-ins extend the capability of Outlook to do new things. A common example of this is the Teams add-in which enables you to create Teams meetings right from within Outlook.
Problems with Add-Ins
Sometimes an add-in can crash or cause issues with Outlook. You may receive an error message every time you open Outlook similar to below:
To rectify errors like this you need to find the offending add-in and disable/remove or reinstall it.
Often these add-ins are installed automatically with other software (eg. Skype) and if you aren't actively using the functionality you can safely disable them.
If you aren't sure which add-in is causing the errors you may need to disable them all, then enable them one-by-one to pinpoint the one that is causing the errors.
How to disable add-ins
To disable add-ins first go to File, then Options
Then click on Add-ins, and click the Go button
In the next window you can untick any add-ins that you do not need or that you suspect are causing issues with Outlook. Unticking them will prevent them from loading when Outlook
Re-enabling an Add-In is the same process but tick the box.