On the HP-UX hostA, the command rlogin hostB generates the error "rlogind: Host address mismatch" even though the hostname & IP of hostA are defined in the .rhosts file and the /etc/hosts files of hostB respectively. The IP and the hostname of hostB are defined in the /etc/hosts file of hostA.
Check if DNS is messed up and giving you false information (reverse lookup of the IP to hostname and hostname to IP).
If the systems have multiple interfaces, it may be have the wrong info in /etc/hosts for the interface you are going out on/going into.
Also see the same issue on darklab.net - rlogind: host address mismatch