User passwords work for Telnet not FTP

Perplexing problem on Solaris 2.6 with users being able to telnet to box but if they ftp and use the same password they get ‘login incorrect’. Using /etc/passwd and /etc/shadow files. /etc/nsswitch.conf shows passwd = files nis
Their UIDs match on all 3 Suns, and all users are in the wheel group. However, my account works fine for telnet and ftp. I had a user ftp in as root and my account which worked from his PC (Windows 2000). I don’t think I’ve ever seen this problem before; they either both work or both don’t…… Thanks very much!!!

Regards,
David