Ok some things to do:
1. The card should be formatted using type: FAT (not FAT32) on a PC.
2. Try formatting the card in another device like camera using a xD or SM card.
3. Try formatting the card in the EBW1150 device itself (i.e. before power on; hold the page down button and while still holding it power on; Arranging your Bookshelf message appears; then tap menu (little ebook guy at top-left), then info, then more, then more again. Tap erase external to format the card. Be careful here! Turn off to exit this special mode)
You may already have done these things, but that's all I can think of doing to get the card recognized by the ebook reader.