I've now proved that the BT Home Hub 3 won't work with the TP-LINK PS110P Parallel Print Server.
This is what I did to proved it.
1) I set up the Print Server on my Netgear Router and everything works fine.
2) I transfer the cables from the Netgear Router to the BT Home Hub 3 Router and try to print. No joy, only error messages.
3) I transfer the cables back to the Netgear Router and everything works fine again.
Conclusion: The BT Home Hub won't work with this Print Server, so unless someone knows better, I will be using the Netgear Router from now on.
BT, why can't you supply a router that will do the things that other routers will do?
The problem is now sorted.
I had entered the wrong IP address on one of my computers. The Netgear router was still working with the 'incorrect' setting but the BT Home Hub wouldn't. That's what confused me.
My apologies to BT