So one is led to believe but this is wrong!
I'd already tried setting the ip addresses to match, as per the manual (and your post) but that did not work.
It ended up being a specific combination of running firmware update, running the install off the CD (as NAS Navigator would not accept ANY password and/or gave the generic error message as per my first post.), then changing the ip address on the PC to match the network, rebooting the PC, rebooting the linkstation and then updating the IP address on the Linkstation. It was the most convoluted process I've ever had to go through and the tech support and instructions from Buffalo are abysmal.
Thanks for your post anyway Paul.
Regards
Brian