The Microsoft DNS services are meant to map the computer's name to its dynamically assigned IP address from the DHCP server. If your DNS server caches the IP addresses assigned to computer names and are not refreshed at the same rate as DHCP, then you will get these problems.

Try changing the 'Lease Time' for your DHCP Server and make sure your DNS server refreshes on a regular basis.  There is an option called 'Always dynamic update DNS A and Ptr records' in the DHCP setup, try enabling this.

When you connect to a group, AB Tutor uses the computers NAME to make the connection.  TCP/IP then uses the DNS server to get the remote machines actual IP address.  Once the IP address is return, the connection is made.

When you Scan for machines (via the group), the program sends out a message on the network asking for the details of any running machine that have the client program installed.  The remote machine then sends back its computer name and current TRUE IP address.

Hence all connections are correct.

Now if your DNS server is not synced with your DHCP server then the IP address assigned to a computer name could still point to an old IP address assigned to another machine.

You can test this by opening up the 'Command' prompt window on the tutor machine and typing 'nslookup ' and press return (where is the actual name assign to one of the remote machines that connects incorrectly).

Now go to that remote machine and logon, go to the ‘Command’ prompt windows and type ‘ipconfig’ and press return.  You will probably find that the IP addresses are not the same.

Now go back to the Tutor Machine and in the Command prompt windows try typing 'ipconfig /flushdns' and check the IP addresses again.

If this is the problem, then you must make sure your DHCP/DNS servers are sync and refresh at the same time.