Glow, the message is " enough rule " or , enough Fuel ? Enough fuel , i've already seen that. i have often 2.3% fuel remaining when i have finished the saturn injection, sign that the fuel consuption is high. You can see that on the main MFd, there is a line about it.
This is all the fun about this game, and the actual difficulty of space flight. I have the same problem today with my flight to pluto.
If u have saturn visible, try to fly to it without orbit planner, and with time compression. Dunno why but the fuel remain stable. U see saturn going to the side , u stop the time compression, you aim your spaceflight again to saturn and repeat the manoeuver.