I believe it won't plot beyond 100LY's & I too had trouble getting it to plot when the destination is beyond 60LY's, my friend kept saying just wait, it will update, but many times it does not, so this is the trick I found works every time.
In your galaxy map, click on Navigation. First thing CHANGE JUMP DATA TO FASTEST ROUTES!! In the search box at the top, type in the system name you want (must be spelled exact). Once the map adjust to that location, select it (puts the orange marker over it). Now hit the current location arrow to bring the map view back to where you are (with a blue marker over it).
Now use your left & right mouse buttons to line up the blue & orange markers.. blue in the foreground, orange in the distance. Using your W key & right mouse button, begin to move the map view toward the orange marker. As you do this, hover over systems, you will notice the plot is available. Keep moving toward your destination & hovering over systems. This seems to update my ships plot computer more quickly. Once it no longer shows a plot course, I usually choose a system close to the destination it if is beyond 100LY's.
Sounds like a lot of work, but it only takes like 15/20 seconds to do this. I hope they get this fixed in the next patch. Hope this helps.
UPDATE: disregard & read post #8