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Strange waveform on oscilloscope from pci6534 output

Hello all NI experts:
Please help. I have tried to search the forum for solution but I cannot find it. Please help me.
[ Problem ]
I am currently having  a  problem with PCI-6534 output waveforms.  I am doing a simple test:  "generating CLK and output signals and then verifing these signals on the oscilloscope".  I got the CLK signal works, but when I want to output '11111111' in port DIOA0 (which means making DIOA0 remain  HIGH), I got some strange output '110011001100' in port DIOA0. Would you please tell me why this happens?? Is something wrong with my code, configuration, or H/W problem?? How can I solve this problem??
This is the waveform I got from the oscilloscope (Sorry I could not attach my jpg here! I hope this is clear)
REQ:      01 01 01 01 01 01 01...
DIOA0:    01 10 01 10 01 10 01... 
But I expect to get the following waveform
REQ:      01 01 01 01 01 01 01...
DIOA0:    11 11 11 11 11 11 11...  
PS. I must control the PCI-6534 using Matlab (I can not use Labview or other software).

[ NI Driver ]
NI_Driver: Traditional NIDAQ 7.4

[  My Configuration ]
I am using PCI-6534 to generate some patterns therefore I configure it as "Pattern Generation Mode" and I  am using the internal clock as my clocking source.

[ My Matlab code ]
my_count = 100000;
my_array = ones(1,my_count,'int16');  <- generate [1 1 1 1 1 1 1 1 1 1.....]

%% Load library

%% Display the list of available functions
% libfunctionsview('myni')


calllib('myni','DIG_Block_Out',1,1,my_array,my_count);  <- This is supposed to make DIOA0 remain 'HIGH' (which means output '1111111'), right??


%% Unassign any 'previously assigned ports' to group
unloadlibrary myni
Thank you in advanced
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Hi Egret,

It looks like you've configured the 6534 to generate only on one byte-wide (port), but your data is two bytes-wide.  Either change dig_grp_config to use two ports or change your array to be a byte wide. 

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