The C shell could not find the program you gave as a command.
Check the form and spelling of the command line. If that looks correct, use echo $path to see if the user's search path is correct. When communications are garbled, it is possible to unset a search path to such an extent that only built-in shell commands are available. Below is a command to reset a basic search path:
% set path = (/usr/bin /usr/ccs/bin /usr/openwin/bin .) |
For more information about the C shell, see csh(1).