I pasted what you have in and got the same error you did. then I changed the quote marks and it created the curves just fine.
Try this instead:
GRAY_CURVE="0;0 2;5 5;12 10;21 20;40 30;57 40;69 50;77 60;81 70;84 80;87 90;92 95;95 97;97 100;100"
Hope that helps,
Richard Boutwell