So you can't have the same enchant on a weapon multiple times, but does that count for enchants that are variable, like Bane? Basically, could you have a +1 Bane (Undead), Bane (Demon), Bane (Dragon) weapon?
Those are fine. As each one is a separate enchant.
Some may be variable but would conflict. Patriotic for example, has you pick one country to align to. A GM would be well within his rights to limit that as its wording suggests it should have a limit of one.
just a note too about that. If you have bane evil outsider and bane demon and you fight a demon that is also an evil outsider you only get +2 to attack and 2d6, not +2 and 4d6. This is in a FAQ or book where they introduced other bane-like enchants.