Athmospheric modification Plant research

Are you playing the stock retail game (v 1.44) or with a mod?

In stock, which I play, the max level of the Atmospheric Modification Plant is 20, and is gained while researching the Planet Utilization tech.

1.20!?
That is most likely the problem right there.

Yes, the 1.44 patch should work with it.

I originally had 1.35 purchased from a store, and the 1.44 patch cured a few bugs and annoying little problems, so for you, going from 1.20 to 1.44 should cure a lot of problems and improve assorted things.

Level 40 Planet Util will max it out. 0.5 years is the best for atmospherics (heh!)