Aircraft Dissapearence

I have a problem. I just started mid-world in r-delta, leased some 737-700's for delivery, and I still had some money left. So I scrounged around in the used market and bought another 737-300(it was my starter). I configured the seat configs as so, and I went to my Denver-Albany route. I added weekly flights and pressed "add flights". It loaded and said something like "please select an aircraft do do the routes". I was confused, so I went to do it again and the 733 was missing. I checked the Aircrafts page, Airline page etc. and couldn't find it at all. After talking to people in chat this was the best option. I don't know what happened and I'm still confused. I originally had 2 733's, my starter, and the one from the used market.

I don't have the airline anymore.