OK. It took a couple hours but I remembered why I set the ACR resolution to 1px/in. If you leave it at the default 240px/in, then open the image in PhotoShop and try to crop by entering 1024inX768in (the default is inches) PS tries to generate a file that is 1024X768 inches at a resolution of 240 dpi. This would be about 45Gb and you'll probably get an error message saying unable to complete task because the scratch disk is full.
Setting the crop size to pixels instead of inches would also prevent this from happening.