Colonizing too rapidly ...

[Suicide Junkie]

Well, when I played, I'm sure I wasn't going about the population movement in the most efficient way.

I ended up with 90% of my vehicles warping out in the Last 3 months. After that, I think I had no planets for a while, and pushed out the Psy guys to the south to make a home.

The economic struggles were great, though: I had 30 Powerful Dreadnoughts in mothballs, but I could only afford to maintain three for the longest time. I had to use cheap fighters and sats as my primary defense, and used the dreads to soften up the 10-20 baseship fleets the Psy guys were sending in.
I also had to glass the first few planets I was going to colonize, so their value was horrible (glassing damage was increased, I believe)
Eventually I got the value back up, and a few planet captures, and cleared out the rest of the aliens from the system.