Not having seen this error before and stating you didn't think it was a variable, only shows that you have never exceeded the limits... Yes FP has limits, though adjusting the display limits, should solve the problem.. When I say limits, I mean defaults.. If adjusting the display parameters, doesn't work, my guess is you have not increased it enough. It helps to take note of the number FP is attempting to generate, in the Stats and make sure you, increase it to a number that is higher than that... My way of solving this error, which I have seen on many occasions, is to just add two zeroes.
For example if your display number is 50,000 I would change it to 5,000,000.. Overkill maybe.. and there are other things you can do, to optimise FP, but 9 times out of 10, it solves it for me.
One thing... When you hear that FP can generate millions of objects, maybe even billions, it depends on the detail in those objects and how many you want to scatter... and obviously how many scatters you have and how much memory you have, for rendering... memory, depends on whether you use cup or gpu, if it's gpu, then you are relying on graphic card memory.
Anyway, just tweak the Display Parameters again and it should work.