"Deleting Hull model elements is not allowed" in Hull Design

I have a few empty hull blocks in a project that I would like to remove. But even as SYSTEM when I try to delete them in Hull Design I get the message "Deleting Hull model elements is not allowed"
Why is it so and am I in any way able to delete them?

maybe you have status controller object defined on BLOCK element?

Access Control Rights (ACR) Activation, please check with your administrator.

unless you tried to delete hull element by using right click mouse menu in design exlorer, ..that is no no!