"set_analog_pullup" Not Working

I wrote some code just to simply get the readings from the ET sensors on the front and back of my robot. The one on the front is plugged into analog port 7, and the one on the back is plugged into analog port 1. I know that to get readings from the ET sensors, you need to set the "analog pullup state" to 0, so here is what I wrote:

#include

int main()
{
set_analog_pullup(1,0);
msleep(20);
set_analog_pullup(7,0);
msleep(20);

while (a_button() == 0) {
set_analog_pullup(1,0);
set_analog_pullup(7,0);
display_clear();
printf("Front value at %d\tBack value at %d\n", analog(7), analog(1));
msleep(1000);
}
return(0);
}

When I run this program, the display on the Link just gives me "Front value is 889, Back value is 889" or something like that--as if I had not enable the pull-up resistors.

I am not an extremely good programmer, but I do have some experience. I also have some experience programming with the KISS IDE and the KIPR Link. This is my first attempt at programming with ET sensors.

Another thing, too--the ET sensors DO work. I went to Home>Motors and Sensors>Sensor List to view the readings from analog ports 1 and 7 and clicked "Toggle Pull-up" for both of them and I got good, accurate readings from both of them. So I really don't understand why my program isn't working, because from everything I've read on this website and on the "Getting Started on the KIPR Link" pdf file, the above program should work.

Thanks for anybody who helps! This problem is preventing me from doing anything with the sensors.....