In the Domain Manager i put in z.4invisionfree.com and a message came up this is what it said You can not use a sub-domain of InvisionFree.com at this time. What does this mean?

You cannot make an sub domain by InvisionFree at this time, it's been like that for few years, And in your domain manager, your supposed to put in your domain (.com/.info etc..) or you can get an free sub-domain from an offering service.