Ensure that you have a variable that for group.This variable should have capture each alternative for each of the choice set to give each a unique identy.For instances (1,1,1) ......(n,n,n) where n denotes the last individual and the corresponding choice sets.Then include the new variable into the command.
I noted that it still says At least one group has more than one chosen alternative even in cases when an individual does not choose either of the two options 0, 0