At first thanks for this tool : it is really useful !
I've encountered two BPC V4.2.1.0 freeze when I tried to update commodities prices from "Grid Update", just after hitting "Save Data". (can't do anything in the window and move or close it, needed to kill it) Before that I haven't got problem to make this and it work after.
Also, the calculation of "Amount" to take in different station don't consider "Avail Stock"...
Could it be the station data you have is outdated?