Ok, just had this issue in 0.51.
Have 8GB of RAM and wasn't playing too long in this session. Actually, i only recently reloaded. Also, never had this issue before in either 0.50 or in FA. Restarting game fixed it. Unfortunately, I saw too late that you guys need debug.err file. I'll provide one if I run into this again.
Btw. I have played on huge maps in FA with Stromworld mod and 28 factions in one game. Even after 500 seasons it was running smoothly and no memory issues. I seriously doubt its low memory issue here.
Edit: I also remember that steamer MadDjinn ran into this on his first play of LH. Actually he had it at the very start of the game. So I really really doubt he ran out of memory at the start on a large map with 8 factions.
Edit2: Here is a link to a recording of that stream - http://www.twitch.tv/maddjinn/b/380965967 . It's around 15-th minute that he ran into it.