Probably a password issue.
In order to be able to login through AFP, the user must either have the
simple password set or you must have universal password enabled so that
you have the same password for AFP as for Windows machines with a Novell
client.

Yet another possibility is to use the CLEARTEXT option as described in the
documentation here:

http://www.novell.com/documentation/oes/native/data/ac1pdri.html