Fieldtrip ft_sourcestatistics on volumetric data

Hi there,
I am trying to use ft_sourcestatistics on volumetric data with the following MATLAB Preformatted textscript
data link: dataFT.mat

script:

load dataFT.mat
% build the experimental design and analysis parameters
cfg                     = [];
cfg.dim                 = FT{1}.dim;
cfg.method              = 'montecarlo';
cfg.statistic           = 'ft_statfun_depsamplesFunivariate';
cfg.parameter           = 'mom';
cfg.clusterthreshold    = 'nonparametric_common';
cfg.correctm            = 'cluster';
cfg.computecritval      = 'yes';
cfg.numrandomization    = 1000;
cfg.tail                = 0;    % Two sided testing
cfg.clustertail         = cfg.tail;
cfg.correcttail         = 'alpha'; % basically bonferroni correction
cfg.alpha               = 0.05;
cfg.computeprob         = 'yes';

% design matrix
nsubj = numel(unique(FT(:,2)));
nrows = numel(FT(:,1));
cfg.design = zeros(3,nrows);


% subject id
cfg.design(1,:)           = repelem([1:nsubj],nrows/nsubj);
% Stim: real, sham
cfg.design(2,:)           = repmat(repelem([1:2],2),1,nrows/4);
% order: pre, post
cfg.design(3,:)           = repmat([1:2],1,nrows/2);
% maybe flip it?
% cfg.design = cfg.design';
% row of design matrix that contains unit variable (subjects)
cfg.uvar                = 1;
% row of design matrix that contains within-cell variables 
cfg.wvar                = 2; 
% row of design matrix that contains independent variable 
cfg.ivar                = 3;
% source statistic analysis
[stat] = ft_sourcestatistics(cfg, FT{:,1});

but I get the error:

Error using resampledesign (line 153)
the design matrix variables should be constant within a block

I think my design matrix is fine, because I have 52 participants with 2 within-subject factors.

I really appreciate your helP!

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