ARD 3.8 DNS / Cache not updating

Hello,

Basically a lot of my clients often show as "offline" when looking via Apple Remote Desktop. If I right click the troubled client, and press "get info" I can see that the machine name and IP are not correctly matched. If I ping the machine and get the correct IP, I can paste this into the "get info" window and then things work fine.

My question is - why is this happening? And what can I do to fix it?

I assume its DNS, but where to begin.

thanks