Hi Luciano,
As you can see in our documentation, it's not possible to have a theme's menu webblock  (that will be used in scaffolding patterns) that is connected to reference entities:
https://www.outsystems.com/help/servicestudio/9.0/User_Interface/Design_Screen_Layouts.htm#Design_Menu_Layout

What I would do is just manually copying the menu webblock to the BackOffice module, and change all the menu items to refer the new pages' url/names. You can add records in the FrontOffice's MenuItem entity to include those pages.
Does this help?

Best Regards,
Vasco Pessanha

In attachment you can find a simple application with two modules - FrontOffice and BackOffice - each one using its own menu webblock. I followed the copy/paste approach ;)
Hope this helps you!

Thanks Vasco. It is working but I am not enable to access the site properties available on the first eSpace. I think that site properties must be available to all eSpaces. I tried to find out some references and nothing. What can I do to fix that ?

Hi Luciano,
Yes, it's true, you cannot access site properties in other modules. You can have a public action in the main module that returns the value of a site property but what is your scenario? Why do you want to use the site property?

Best Regards,
Vasco Pessanha