Marsbar error: No valid data for roi

Dear Experts,

I am performing a ROI analysis by using marsbar. I define 5 ROIs as five
different single voxels. After setting the desing I extract the data from
each ROI. Everything works fine for 4 of 5 ROIs. For the fifth ROI (i.e.,
a single voxel having MNI coordinates -42 -6 56) I get the following
error:

MarsBaR analysis functions prepended to path
Loaded MarsBaR defaults from base defaults
Design reporting                        :                        ...done
Fetching data                           :                         1/1
Warning: No valid data for roi 1 (points_coordinate_mm_-42_-6_56)
> In maroi.get_marsy at 80
  In m                       ...done
??? Function 'block_rows' is not defined for values of class 'cell'.

Error in ==> marsbar at 976
marsY = block_rows(marsY, row);

Error in ==> spm at 857
evalin('base',CBs{v-1})

??? Error while evaluating uicontrol Callback.

Could you tell me which is the origin of this problem? And, How can I fix
the problem?

Many thanks in advance.