Hmmm, that's very strange indeed. I do believe the range is limited with the Terror Star, but the range limitaion would/should prevent the Terror Star from even entering the sector that the star systems are in, not from letting it get close and not be able to attack. I remeber two or three games ago, I tried to send a Terror Star to the opposite end of the galaxy, and I got the "that's too far from one of your planets or starbases to travel to" message. I put a couple of starbases to make a 'route' to get there, and then the Terror Star was able to go there. But I've never encountered a fully-functional Terror Star that wasn't able to attack systems once I got the ball rolling.

I'm completely stumped.

Sorry I couldn't have been more helpful. Good luck, and if you figure out what caused this to happen, let all us folks at these boards know, so we'll know what to do when/if we encounter Terror Star duds in our own games in the future.
Good luck.

-GeorgeT