Well then..that still stinks!
If the guy is not eligible, then they shouldn't allow you the option then (or have him shown on your roster) UNTIL the day he is eligible to be inserted. It would possibly stop any confusion.
I just assumed that since he was listed as being on my roster that Saturday morning that I could insert him that day.
I also, that same day as Bay, picked up Detroit's SS Guillen. But they waivered him until Monday. He is on my roster now. That is what confused me. I picked them both up at the same time; but they waivered Guillen, but listed Bay on my roster Saturday morning.