That is very strange. I'm not sure what to think. The fingerprint reader is not involved in the sketch at that point. After you enter the ID number, the sketch does this:
- Code: Select all | TOGGLE FULL SIZE
Serial.print("Enrolling ID #");
while (! getFingerprintEnroll(id) );
So, if it's reading the number you enter, it should print "EnrollingID # nnn" before it ever goes to read the fingerprint.
You are entering a number for the ID, right? The sketch wants digits. But, even if you are not entering digits, it should still print "Enrolling ID# 0".
EDIT: Aha! Are you hitting the return key after you type in the number? Just clicking Send might not be enough - the sketch wants to see a non-digit before it will get out of the loop where it reads the ID number.