May be you have plotted to a non interactive termial about gnuplot_kernel HOT 1 CLOSED

That is just an inaccurate error message. The real problem is that you had bad gnuplot syntax i.e. title="blah blah" instead of title "blah blah", to which gnuplot complained "invalid expression". What the kernel sees is a plot command, so it prepares an image file for gnuplot to print to; , gnuplot draws nothing because of the bad syntax and the kernel reacts to something wrong but not sure what it is.

I will add this case to what could have gone wrong.

from gnuplot_kernel.