Lion clients unable to connect to Snow Leopard server
If you are attempting to connect from a bound Lion client to a bound Snow Leopard server you must use the FQDN for the server.
For example: servername.yourdomain.com
If you don't, you may receive an error "The version of the
server you are trying to connect to is not supported. Please contact
your system administrator to resolve the problem."
Also check what authentication method you are using.
- Open Server Manager
- Highlight "AFP"
- Click on the "Access" tab
- Change "Authentication" to "Any Method"
Attempt to connect from at Lion client using the FQDN of the server.
Note: changing the authentication to Any Method can possibly break
single-sign-on for Snow Leopard client. If this happens, change the
authentication to "Kerberos". Lion clients should still be able to
access the server.
Apple kb on issue: http://support.apple.com/kb/TS3861?viewlocale=en_US