For an unknown reason the user.config file of the Outlook Addin can get corrupted. For example, it may contain only white spaces. This resulted in the Addin failing to load and therefore set to inactive and loadbehavior set to 2 (on-demand) rather than 3 (load on startup).
The resolution is to:
- Rename/delete the user.config file from c:\users\<username>\AppData\Local\Microsoft_Corporation\.Soup Mail Outlook Addin <some guid>\<folder with latest modified date>\user.config.
- Update registry key at: [HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins\Soup Outlook Addin 2007] "LoadBehavior"=dword:00000003
- In some occasions might also require the toolbar be be manually re-enabled in Outlook > Trust Centre > COM Addin > Tick to enable and click ok.