The problem is that you've run out of memory. So if you are using a 64-bit Windows, and a 32-bit Calibre, switch to a 64-bit Calibre. If that isn't possible because you are on a 32-bit Windows, then you are out of luck. If you can move to a 64-bit Calibre and you still run out of memory, the only option is to add more memory to your computer.
Now I noticed something you don't want.
Code:
'pdf_page_margin_bottom': 72.0,
'pdf_page_margin_left': 72.0,
'pdf_page_margin_right': 72.0,
'pdf_page_margin_top': 72.0,
For these images, you don't want any margins as all that will do is make the images smaller.