Welcome to LQ.
""TCL script to drop down the packets in particular link at specific time""
$ ns drop1.tcl : Works OK here. Nam opens.
But : If you are doing the command 'ns drop1.tcl' as root (su),
do not expect a GUI applications like nam to work.
The default location for ns-allinone-2.xx is /home/<name>/<dir>/.
And all commands are to be run as unprivileged user.
Good luck !