Non-planar robot Dynamics error using Roy Featherstone's Spatial toolbox

I am using this code to test robot dynamics of above robot using Spatial Toolbox:

FDab(rob, [0;0;0], [0;0;0], [0;0;0])

But it gives error:

Error using  *
Inner matrix dimensions must agree.

Error in FDab (line 49)
    a{i} = Xup{i} * -a_grav + c{i};

This is because Xup is 6x6 double whereas a_grav is 1x3.

The 3 link non-planar robot is given as:

    rob.NB = 3;
rob.parent = [0:2];
rob.jtype = { 'R', 'R', 'R' }

model.gravity = [0 0 0];

rob.Xtree{1} = rotx(1.57) * xlt([0 0 0]);
rob.Xtree{2} = roty(1.57) * xlt([0.15,0,0]);
rob.Xtree{3} = xlt([0.34 0 0]);

ax1=0.03; ay1=0.03; az1=0.03;
ax2=0.28; ay2=0.05; az2=0.05;
ax3=0.2; ay3=0.05; az3=0.05;

rob.I{1} = mcI( 1, [0 0 -0.02], 1/12*[ay1^2+az1^2 0 0; 0 ax1^2+az1^2 0; 0 0 ax1^2+ay1^2] )
rob.I{2} = mcI( 4, [0.14 0 0], 4/12*[ay2^2+az2^2 0 0; 0 ax2^2+az2^2 0; 0 0 ax2^2+ay2^2] )
rob.I{3} = mcI( 3, [0.1 0 0], 3/12*[ay3^2+az3^2 0 0; 0 ax3^2+az3^2 0; 0 0 ax3^2+ay3^2] )

rob.appearance.base = ...
  { 'box', [-0.2 -0.3 -0.2; 0.2 0.3 -0.07] };

rob.appearance.body{1} = ...
    { 'cyl', [0 0 0; 0.11 0 0], 0.05, ...
      'cyl', [0 0 -0.06; 0 0 0.06], 0.06 };

rob.appearance.body{2} = ...
    { 'cyl', [0 0 0; 0.34 0 0], 0.05, ...
      'cyl', [0 0 -0.06; 0 0 0.06], 0.06 };

rob.appearance.body{3} = ...
    { 'cyl', [0 0 0; 0.26 0 0], 0.05, ...
      'cyl', [0 0 -0.06; 0 0 0.06], 0.06 };

showmotion(rob)

How can I overcome the error?