It seems you are not concatenating a column table...so the error.
col1 = rand(10,1) ;
col2 = rand(20,1) ;
row1 = rand(1,10) ;
T1 = table(col1) ;
T2 = table(col2) ;
T3 = table(row1) ;
%
T1.Properties.VariableNames = {'column'} ;
T2.Properties.VariableNames = {'column'} ;
T12 = vertcat(T1,T2) ; % no error
T3.Properties.VariableNames = {'column'} ;
T13 = vertcat(T1,T3) ; % error
