The error message is related to a security feature that was added in ASE 15.7 SP50 / SP100 involving a "hosts.allow" file to control the ability to make remote dumps. See "Remote Dump Host Control" for details.
The initial implementation had a bug, CR 749101:
"The connection to a backup server can be rejected if the client host has multiple IP addresses and the entries in the target backup server hosts.allow file are not authorizing the first remote IP address. Likewise, the connections will be rejected if the host name used in the first column of the hosts.allow file specifies a host alias different from the actual host name"
Now, the fix for this bug was released in SP121, so it seems it hasn't resolved every possible.
Have a look at the contents of your hosts.allow (default location is $SYBASE) and try modifying the contents to include any aliases your host might be configured for that are missing.