Thanks for the suggestion zhu.
I checked and there were no blank lines in the sch file.
My problem was that I had the data plots in the schematic file and there was too much data to display.
I moved the data plots to a data display (dpl) file and the schematic would open. QucsStudio then crashed when I tried to open the dpl file. It was ok if I deleted the dataset.
Finally I simplified the data display to reduce the number of plots that I had. Now I can run my 5000 iteration Monte Carlo analysis and display the data without QucsStudio crashing.