Maybe you experience the following scenario:
You want to use the Lync/Skype for Business Add-in (UCAddin.dll) within Outlook, but the button within the calendar isn’t at place every time you start Outlook. You go into Add-Ins, check that it is not disabled (Manage: Disabled Items) and then select the checkbox for the Lync/Skype for Business Add-in (Manage: COM Add-ins) and then the button appears again and can be used.
But the next time you start Outlook the button disappeared again.
Now you think that there is a problem with the Add-in and start searching within the Event logs (Administrative Events) and try to figure out SidebySide (SxS) problems, but this didn’t helped out out here either.
SidebySide (SxS) diagnose –> http://blogs.msdn.com/b/junfeng/archive/2006/04/14/576314.aspx
Finally you need to look for two things.
First: Are there any Slow And Disabled Add-ins listed under File – Info – Manage Add-Ins? If yes, than enable the disabled Add-in here.
Secondly: Check the LoadBehavior of the Add-in in question within the registry under HKCU\Software\Microsoft\Office\Outlook\Addins and set it to 3.
Office Add-in does not load –> http://blogs.msdn.com/b/haahmadi/archive/2010/05/26/my-vsto-add-in-does-not-load.aspx