We’ve recently seen a plethora of issues with Office Timeline ribbon not getting loaded (again?…)
In the end, it seems they’re all related to abused systems. Once the customers reinstalled Office 2007, the add-in loaded fine. Thank God the customer had this idea before we had to present it to him (nobody likes to be told “uninstall A,B,C” and then “install Office Timeline”, although in many situations this fixes the problem (we call this troubleshooting procedure “the silver bullet” – give the customer TSB 🙂