Hi Sebastian! I've found the issue!

The problem is that when you add a shared module it is added on ModulePermission table with the same ModuleId of the original and there is no possibility to create duplicate for RoleId -1 (All Users) for the new portal because now it is a duplicate for primary key of that table (ModuleId+PermissionId+RoleId). To fix sharing modules is needed to add in primary key also PortalId!

also this thing is strange that no one has noticed! ...I begin really to fear of being the only one to use DNN!

Sebastian, do you think that will solve this problem? ... Thank goodness you're here! ;-))

It is the first time I use content sharing between portal groups and I'm struck by the time I saved and the result obtained. I suggest to anyone who needs to content sharing between different portals do not hesitate and use this excellent feature that until a few days ago did not even know existed!

After fixed DB foreign key for ModulePermission table all work fine! I've used it also for sharing Ventrian Property Agent and News Articles modules... all work great!!!