Why am I no longer able to build ships?

For whatever reason, I can't build ships anymore. When the game started I built a scout and colonized a few planets, Then (and I can't be sure this is what caused it) I played around with the ship builder, and now I can't build any ships. The ship name appears in the window, but it says zero weeks to build, and I the purchase button is grayed out.

Anyone have any ideas? I'm afraid it might be some noob solution like "you're out of money, raise taxes," but I can't figure it out.