ARD connection failed to client

Still relatively new to ARD. I have a new lab that I rolled out and am unable to connect via ARD 3.5.1 to the majority of the client stations. The lab was built as follows. We configured one base system and used Carbon Copy Cloner to clone it to the other workstations. After the worktsations were cloned, we used the Sharing, System Preference to change the name of the computer and enable Remote Management for All Users.

We also used the Accounts system preference to change the Full Name of the user to match the name of the lab workstation.

I have no problems accessing the first 4 computers in the lab from ARD at my desktop but when I try to access any of the others, I get "connecton failed to Lab Computer xx", where xx is the system number.

What have I done wrong?

I have been able to use ARD to copy some files to each of the workstations though. Puzzled.

These systems have OS X Lion installed.