Apple Remote Desktop has become flaky over the last few versions of OS X. Apple isn’t really working on it anymore. It is still a great tool, but often, it will have difficulties finding computers on the network. Here is what I do to make it work a little better.
Remove Every Device From The “All Computers” List
First, highlight all the devices in the All Computers list and delete them. Then, quit ARD and move onto the next steps.
Flush DNS and ARP Caches
ARD looks for computers advertising bonjour on the local network. I have found that flushing the cache and removing ARP entries helps ARD start fresh when looking for computers.
Flush DNS Cache
sudo dscacheutil -flushcache
10.7 and 10.8
sudo killall -HUP mDNSResponder
dscacheutil -flushcache; sudo killall -HUP mDNSResponder
sudo discoveryutil udnsflushcaches
Flush ARP Cache
sudo arp -ad
The commands are not guaranteed to fix the issues, but I have had good luck with it. I have also used the commands above to fix the issue of computers in a list randomly changing into a different computer than what was originally added.
Another Trick (Perhaps The Most Useful)
You may also want to restart ARD on the client machines using the kickstart command.
/System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -restart -agent