In the baseline analysis the highest stress is 333 MPa at 44% compression, so the stress constraint should be at least as much in order to give Optistruct a chance for a feasible design. It should be noted that typically porous material represented by periodic lattice structures exhibits lower stiffness per volume unit compared to fully dense material. Lattice optimization gives huge stress (41.000 MPa) at 44% compression. This kind of makes sense because lattice beams are way too slender since even a solid block of material was at the limit of feasibility. So this high compression % cannot be handled by such a lattice structure (even before buckling is taken into account).
The *** INTERNAL PROGRAMMING ERROR *** is a strange one. Perhaps it is a software bug that should be handled by Altair, as suggested in the following topic:
Looks like the issue is already resolved in 2017.2.2 version:
Running linear static analysis instead did not give such error, but can't be used in your case as it gives too high stresses at larger displacements.
I also noticed unit inconsistency: on DTI_units mass was set to kg, but the mass of aluminium is 2.7e-9 so it should be Mgg (tonne) instead.