Photoshop—"scratch disk is full" error Using a Macbook Air, I have 60Gb free space on my hard drive, yet I can't crop an image (W x H, Resolution setting) because "the scratch disks are full".

What does the error mean? How do I fix it? I can't imagine Photoshop's doing an operation that requires more than 60Gb of spare disk space...
I found this guide here with a simple Google Search. 

If you are getting a "scratch disk full" error when attempting to crop an image, you probably have accidentally entered the size and resolution values in the options bar for the crop tool. You could have also possibly entered the values in the wrong units. This can cause massive render issues as it will try to generate an incredibly large file, ultimately causing the error. The solution to this issue is to press clear in the options bar after selecting the crop tool, but before you drag a crop selection.