No Properties

I have installed the Requirements Viewpoint. Things were OK with my project and then this morning I am unable to view the Properites of any object in the project I was working with (Toy Catapult tutorial). In the Properties tab I get the following message “Properties not available.” when I select any object. In the Information tab I get the following error :“ExtensionPointHelper.createTypeInstance(…) _ Unable to instantiate class type:org.polarsys.capella.vp.requirements.Requirements.provi der.CapellaRequirementsItemProviderDecoratorAdapterFactory | Error | | null | | | 8:15:39 AM”.
The In-flight Entertainment System tutorial appears fine.
I have tried removing and reinstalling the viewpoint, neither action fixed the problem.
Your Help would be greatly appreciated. I am most of the way through the tutorial and would rather not have to go back to the beginning.
In His service,

Could you precise which version of Capella and which version of the requirement add-on you are using?