This is a recurrent issue: “my SD card won’t work, I tried the sample, I triple check hardware, it just won’t work”. The main problem here it’s hard to get feedback and report it to jallib library’s author (namely Matt). Different issues were previously found:

• some brands seem to work better than others. For instance, SanDisk is reported to work nice, whereas there seems to have troubles using Kingston’s.
• some SD cards will require pull-up resistors, some won’t.
• and SDHC, high capacity SD card, aren’t supported.