I think I may have just figured out my problem -- there was only 1.85MB free on the SD card. Upon opening it on my PC to move everything over so I could format it, I noticed an empty "temp" directory that wasn't on there before, then I noticed the extreme lack of free space. I'm guessing WAD Manager has to decompress the WAD contents onto the SD card during installation, or something similar, and it simply did not have enough free space to complete this. This would explain why it failed part-way through the installation instead of immediately. I'll skip #2 for now and jump straight to #3 after deleting some files. Wish me luck!