setting max_allowed_packet dynamically problem

[List Man]

I am running Server version: 5.1.45-log MySQL Community Server (GPL) and I attempted to
change max packet with the following:  SET GLOBAL max_allowed_packet=16*1024*1024; but it
did not work properly.  The configuration did not change by using the show variables
command.  I changed the configuration file (my.cnf) and restarted the server and the
variable stayed the same.  Does anyone have any ideas?

LS