Error in the Export of the SubModelPart

[GianmarcoBoscolo]

I create a submodelpart. I ha ve to export its nodes and elements. In the .mdpa the relative elements are defined twice: one in the main part, and one in th esubmodelpart. When I run Kratos this gives the following error example:
"Error: attempting to add a new element with Id :1, unfortunately a (different) element with the same Id already exists".