You must have a limit provided for each value. 0 is for unlimited. If you use a 1, that would mean only one person can choose that option for that event, so I highly doubt that is what you want. "1" does not mean that a user can only choose one item from the dropdown... selection limits are how many times each value can be selected throughout the event. If it does not matter, use 0. There should be a | between each limit, with no spaces on either side of the | and you should NOT have a | at the end.
Be sure to watch our video tutorial on custom fields as all of this is covered. Thanks!