ga is a strictly feasible algorithm with respect to bounds and linear constraints, so if you give bounds properly, you will never get a member of a population to violate the constraints. Therefore, you did something wrong.
You don't provide the exact commands that you use, so I am going to have to guess what you did. I suppose that your problem has at least two dimensions, and that you gave the following bounds:
lb = 0;
ub = 5;
lb = zeros(N,1);
ub = 5*ones(N,1);
Here N is the number of dimensions of your problem.
Good luck,
Alan Weiss
MATLAB mathematical toolbox documentation