1. Theres a chance your SD card is not being recognized if left in the PDA for long periods of time. Try removing your SD card and try again.
2.This can also happen if your card was formatted with FAT32. Palm devices are not able to read cards formatted with FAT32. Please reformat your card to FAT/FAT16, then update Principalm again.
Windows Mobile supports both Fat32 & Fat16.
3. It can also be caused by cached library files. Try deleting Principalm from the PDA then insert the SD card and try again.
Also make sure there is data on the card.