You should NEVER partition the Cybook internal memory, or you will may lose the capability of using the internal memory on the device.
You should never play with partitioning on theses device..
The only way I know to correct if it was done, is by command line under Mac OS X or linux by creating the filesystem on the "root" device not the partition
ie under linux
instead of /dev/sdd1
(the device name is ONLY given as an example)