I converted them to 24 bit but now instead of having an error the process is instant and the resulting file is only 1 kb, like there is nothing in it.
The bmp image has to be 96 dpi to. You can change this in gimp to by going to scale image and you will see the scale DPI or something.
I have had the same problems as you, Billman. For some reason the megapack is extremely picky!!
I never had luck converting an image from 16 for example to 24 bit and it ever working right with megapack either.