Advantech PCI-1710 FIFO Problems

I apologise if this is off topic but this ng seems like the best bet.

I have an Advantech PCI-1710 12-bit A/D card that I am trying to get
going. I am supplying the card with a 1Hz 20Vpp sinusoid. Now in my
QuickBasic application, if I print the high and low captured bytes to
the screen in a stream, I only see the first one changing - for
instance, if my code is

highbyte% = inp(a2dhigh)
lowbyte% = inp(a2dlow)

then I will only see the highbyte changing, in its 4-bit range.
Likewise if my code is

lowbyte% = inp(a2dlow)
highbyte% = inp(a2dhigh)

then I will see the lowbyte changing in its 8-bit range. I am
convinced that the problem is related to the FIFO but I am stumped as
to how to solve it. Any help or recommendations would be
appreciated...