This is me again. I have managed to resolve my problem by myself and thought it might us useful to others to know what I did.
As I said I tried to get my Windows 8 desktop to use the printer and it said it was offline. I then tried it on an old windows xp desktop I also have and that did exactly the same thing. My laptop, which I used for the initial full set-up was still working ok.

So what I did was to reconnect the printer to my xp desktop via a cable and got it working like that again. I disconnected it again and put the wireless printer server back in and went through the set up again. This time, instead of chosing the printer from the list (which was assigned to port USB0001) I went for the add new printer option and selected the tcp/ip port that was already there from the first attempt. Hey presto, it worked.

Went through the same process on my windows 8 machine and again, hey presto it worked.

So two points.
1) when you follow the instructions and select your existing printer from the list there must be something wrong with that process. Even though it looks like it is using the new tcp/ip port it still seems to know it was a usb attached printer and is looking for it in the wrong place. No real idea what is wrong but it didn't work.
2) I got it to work by adding a new printer but I used the tcp/ip port it created first time round so I don't know what you would need to do to try to get this working in one hit.

I saw lots of other posts about allocating fixed ip addresses and stuff like that. I didn't need to do anything clever or scary like that just a bit of fiddling and effectively set it up twice on each machine.

Hope this is of use to someone.

Hi, I liked your post but its above my head a bit, what you did. Not sure if you will see this but I am trying to get my WPS510U to work in Win 8.1 and I cannot. It's frustrating! It works fine on Win 7. Walked through the setup & everything and it says it's connected & setup properly, but cannot get it to function. Thanks.

Method 1 – Troubleshooter
The first thing you can try is to run a couple of the network troubleshooters built into Windows 8. A lot of the time, it can solve your wireless or Internet problem for you. To open the troubleshooter, open the search charm and type in troubleshooting. Then click on Troubleshooting, the first option. 

Now you want to click on Network and Internet.

Finally, you will see the different troubleshooters available for fixing wireless and Internet problems. The ones you will want to run are Internet Connections and Network Adapter.

 

Method 2 – Reset TCP/IP in Windows 8
You might also get a message like this when running the troubleshooter:

WiFi does not have a valid IP configuration

In this case, you can reset the TCP/IP stack and Winsock and see if that works. To do this, again open the search charm and type in the command prompt. On the first listing, right-click and choose Run as Administrator.

At the command prompt, type in the following two commands, one at a time and make sure to press Enter after each one:

netsh winsock reset catalog
netsh int IP reset c:\resetlog.txt
Hopefully, your wireless connection is working at this point.

 

Let me know if this works.

 

Regards,
Caleb