Calibre 6.45 on Ubuntu Karmic sees
my SD card on The Pocket Pro.
March 2010 firmware update has been pulled: Buggy
Your file system on your SD card has been damaged.

(4G card with 700 titles...then only 200

)
A Karmic scan did not find and fix
all of the errors

A Windows scan found more
I reformatted the SD card with Windows.
Rolled back the Astak firmware to Dec 2009,
reloaded my books.
All is well