The problem doesn't seem to be the screenmode per se, it's the "couldn't create minigl context" that should give a hint. Are you sure you have a full MiniGL (3D) supported graphics card in your system? Radeon 9250, Voodoo whatever? If not, you might try the "Wazp3D" package from Aminet - at least for testing purposes (because it will be unplayable slow with a Blizzard/Cyberstorm based system).
