We have the same code running on a BitsyX and BitxyXB, the IO are not working for the BitsyXB (tried more than 1). We have the version Windows CE 5.00.51 installed. We also noticed that revision of the SMARTIO is 6, whereas on the bitsyx it is 2, However our code is not using this driver, but directly drives the EIO pins.
On the BitsyXb, you will want to use the DIO driver to drive the EIOn digital I/Os. See topic 1788 for the driver spec. Page 12 lists the driver bit mapping for the BitsyXb ("UCBIO"="EIO").
You can test out the driver on your system with the DIO test app at topic 2164.