RefModificationViolation when changing submodel

I am getting this error:

??? Error using delete
Attempt to modify block in a linked subsystem. This can only be done by the block or its parent through their mask initialization code

When I try to do the following:

b1 = add_block('built-in/SubSystem',blockName);
set_param(b1, **********);

if ishandle(b1)
    delete_block(b1);
end

What could it be?

I have checked and doulbechecked the paths and they all are right, the model is working fine is being loaded fine too, I can not disclose more information because I really do not understand what is going on.