Did you call savemultfigs a second time? Or do you have this error systematically? There is a bug I haven't solved yet that gives this error when savemultfigs is called a second time while the other savemultfigs is still open.
If that's the case, the solution for now is simply to close the gui and relaunch savemultfigs.
Thanks for the comments! I will try to solve this bug and incorporate other useful comments.
my data does not have meaning on negative values, but constructing histograms using kde returns frequencies on negative values and even if I determine the lower limit of x on zero, it returns on zero a big value. (i expect my histogram to start like x^2).