I have found myself the solution to the problem. When the struct rte_mempool *pktmbuf_pool[NB_SOCKETS]; was declared, it was not initialized with NULL and the memory pool was not created because the if clause 'if (pktmbuf_pool[socketID]==NULL)' avoided it.
Once I forced the initialization of all *pktmbuf_pool[NB_SOCKETS] poistions to NULL, then it worked well. Regards, -- Victor