Catastrophic failure when executing linq query in Outlook Add-in

I'm executing following code line to check the passed folder is already available in an existing list.

int foundIndex = folderList.FindIndex(search => search.Folder.EntryID == subFolder.EntryID);

When this line gets executed, an exception as

"Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))" is being thrown. This exception is thrown only when I try to load the add-in through "Manage COM Add-ins" window by clicking on "always enable this add-in" button.

Any idea why this is happening ? I'm using windows 8.1 and outlook 2016.