Cant send UNIX commands via ARD

have you checked to make sure that option is enabled on the client computer?

in ard do you have the client computer selected before trying to click on the send unix command?

can you do other actions with the client?

On the client, apple menu, system preferences, sharing, Remote Management.

If allow access is set to all users, then click the options button.

else, select the user your using to connect to the client, and then click the option button.

Make sure every thing is checked.

click ok

try again on ARD.

Other things to try:

quit and re-open ARD.

delete, then and re-add the client computer from ARD.

unchecking, and then re- checking remote management on the client. (to force the service to restart)