Hello vv01f2009 and welcome to MR..
Although I haven't used a card in my reader yet, I have encountered a few posts dealing with the issue. Run a search to check out other threads.
I did find this thread...
Originally Posted by pwalker8
I have the 2 gig PNY. I generally carry the memory card with me, but don't put it in the 505 unless I need a book that isn't on the 505. I put all my books on the memory card, then put the books that I am either reading, or are on my to be read list on the 505. I do put the card in the 505 every time I add books to the card, just to let it index the card. I do find that when I first loaded the card, I needed to add books in sets rather than all at once, since the indexing software seemed to not be able to handle that many new books at once.
Hopefully someone with more experience will chime in soon..