Linux machine can no longer locate wireless printer

[CharlieH1]

 - System running OK using Linux Mint 17.3 Rosa and printing to wireless printer OK .

- System stops printing and displays error message "unable to connect to printer" when asking it to print a document.

 - Removed printer and reinstalled it.

- Downloaded latest driver version file "hplip-3.17.11.run" via Terminal screen.

 - Chose "GUI Mode" option rather than "Interactive Mode" option.

 - Everything installed OK and was presented with a window "Device Discovery".

 - Opted for "Network/Ethernet wireless network (direct connection or jet direct)" option. Other two options are USB connection (which I've never had on this printer) or "Wireless /802.11" using temporary USB connection.

 - Came up with following error message:

"HPLIP Cannot detect printers on your network

This may be due to existing firewall settings blocking the required ports. When you are in a trusted network environment, you may open the ports for network services like mdns and slp in the firewall. For detailed steps follow the link in http://hplipopensource.com/node/375"

 - Went there but could not find anything obvious relating to this message.

 - Tried reinstalling the drivers again through the Terminal window but this time chose the "Interactive Mode" - which gave me an "0" and "1" option. The "1" being direct wireless connection.

- This brought up an unable to find error in the Terminal window rather than opening the seperate " Device Discovery" window.

- Then decided to reinstall an earlier version of the driver software I still have on my Desktop - "hplip-3.16.7".

 - Opeted for "GUI mode" went as far as the "Device Discovery" window hit the same problem and error message as described above.

 - The only other relevant bits of information I can provide are:

1. Printer is not showing any error messages. I've been through the wireless and network set ups again several times and the test reports print out that everything is OK. I can print staight off a pen drive from a USB port OK but it does not read every file I need as being present so I'm stuck was stuff I need to print but cannot.

2. The following error messages appear at the bottom of the Terminal screen when the "Device Discovery" window cannot find a printer:

"PRINTER SETUP
-------------
Please make sure your printer is connected and powered on at this time.
Do you want to setup printer in GUI mode? (u=GUI mode*, i=Interactive mode) : u

HP Linux Imaging and Printing System (ver. 3.16.7)
Printer/Fax Setup Utility ver. 9.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

(python:13339): Gtk-CRITICAL **: IA__gtk_widget_get_direction: assertion 'GTK_IS_WIDGET (widget)' failed

(python:13339): Gtk-CRITICAL **: IA__gtk_widget_get_direction: assertion 'GTK_IS_WIDGET (widget)' failed

(python:13339): Gtk-CRITICAL **: IA__gtk_widget_get_direction: assertion 'GTK_IS_WIDGET (widget)' failed

(python:13339): Gtk-CRITICAL **: IA__gtk_widget_get_direction: assertion 'GTK_IS_WIDGET (widget)' failed
Searching... (bus=net, timeout=5, ttl=4, search=(None) desc=0, method=slp)
error: No devices found on bus: net
warning: HPLIP cannot detect printers in your network. This may be due to existing firewall settings blocking the required ports.
When you are in a trusted network environment, you may open the ports for network services like mdns and slp in the firewall. For detailed steps follow the link.
http://hplipopensource.com/node/375"

Any help would be appreciated.