Comment 8 for bug 1770027

Hello Edison
Sorry.
 I didn't read that you were using "Alternate Menu for Hplip" and deleting "hp - systray - x".
Your choice as using "Alternate Menu for Hplip" is simple and cool.
 And when I use it ,and disable "HP System Tray Service"(I remove check in autostart) ,the error message (No system tray detected on this system, unable to start, exiting) isn't appeared.

I think that once you have to remove all hplip softwaer and install new one.
how do you install hplip?
On Ubuntu default setting,hplip is installed by apt.
So,Type in terminal
 $ sudo dpkg -l|grep hplip
You see package-name of installed hplip-softwears all.
 $ sudo apt-get remove --purge [Softwear-name]
Repeat until hplip-softwears is gone.

And,reboot,Is the error still appeared?

In my case,latest Hplip(3.18.5) was installed from HP-Web page and Sourceforge.
I type to install it below.
 $ chmod +x hplip-3.18.5.run
 $ ./hplip-3.18.5.run
In install process,it asks uninstall previos-installed-hplip,then answer yes for it.
So Old one will be uninstalled and new only one hplip will be installed.
And try disable "HP System Tray Service"(remove check in autostart).
Good luck!