Choose a random sample of size 20 from 1,2,3,...,100

Using excel 2003:

enter 1 2 3 ... 100 in column A

from analysis tools, select sampling

enter A1:A100 in input range
select random
enter 20 in number of samples
enter B1 in output range
OK

the number 14 appeared twice in column B

Who is at fault: me or excel?

John Adams
Bethlehem, PA