When having a fleet en route to a planet, it happens with at least one random planet per game(? - see below) that the ships enter the planet's area not at the border of the gravity well, but right on top of the planet. The fleet then becomes locked as shown in the picture above, unable to move it anywhere. At that point it's fruitless to continue playing the game, when half of your fleet is inoperable but still using up supplies.

Of course I can't tell if it's only one planet per game, or one planet per system. I don't get that far, because such a 'locking' planet always happened to be just in the same system I started in. Tried reinstalling Windows XP, tried reinstalling the game, nothing worked.