frankly I'm sort of mystified by this message as well. I fail to see how every single planet having its own Huge-hull Battlestation (with six high-cap carrier modules, no less!) and every shipyard having two of said battlestations, and something like six-seven fleets of mixed Large/Meduim ships doing border patrol is 'ripe for conquest,' especially when my medium hulled frigates are happlily slaughtering their way through entire fleets of Large and Huge hulls because the AI apperently cannot into Defenses (hint: ~2000 attack means absolutely nothing when your ship blows up in the first exchange of fire and mine doesn't, because I actually put some ruddy armor, shields and PD on. Fighters just make it even worse, since while the AI ships are happily blowing up the things that'll be replaced next turn at no cost my Missile Destroyer is blowing holes the size of Milwaukee in their ships.)
seriously, I think I get the idea, but it really needs to be smarter about it. but then, the Galciv AI has always made me feel like I was shooting a duct-tape'd puppy when it comes to ship design.