OK.
So, i was a little more invasive then i tend to like to be to try to figure this out. Sorry if it's disrupted some grand scheme of things.
My research behind that error message seems to tie it to the weird bug that developed in the routes table (since i cannot seem to replicate the issue). Basically, from what I understand, it seems it got hung up on a route number and tried to create two or three of route number X (which, it should never. ever. do). Likely having hung up in the middle of inserting the data or some-such. That cascaded down through a few airports and seems to have buggered up here and there a few things, but has been repaired away. (I'm hoping this was the cause).
So, since i couldn't replicate it with my stuff, I logged into your account and tried to replicate it. It seems you have both 747's no longer based out of london Gatwick so i had to make do with Edinburgh - Sao Paulo. It was created with no issues, and i refunded the market research fee (I so hate logging into people's accounts to try to figure these bugs out). I left the route, do with it as you please.
Let me know if it persists though. Definitely.