Re: GaussSum cannot call gnuplot
GaussSum 1.0.5 isn't in Ubuntu so I'm assuming you got it from the GaussSum website. It also would appear that you are using the Windows .zip file. I think you will find that if you install GaussSum from the Ubuntu it will work better for you.
On second thought, it looks more like you are running it in OS X. In that case I'd grab the Linux .tar.gz file from the GaussSum website. If it still can't find Gnuplot, go into File->Settings and change the path to gnuplot.
"That's all very well in practice, but will it ever work in theory?" -- G. Hill
"A tidy laboratory means a lazy chemist." -- Jöns Jacob Berzelius