Code:
#define SPEED_SETTING 150 //forward speed setting (127 to 254)
Code:
if (SPEED_SETTING < 128 || speed_control > 254) //Check speed_setting for valid forward speed
SPEED_SETTING = 150; //If not valid number set to default
You defined SPEED_SETTING as a constant, I believe you can not set a defined constant after you are running the code, also as noted by someone else before, C is case sensative.
Errors in your code I marked in red.