I can convert a cell array of matrices to matrix:
>> C={[1,1]; [2,2]; [3,3]};
>> cell2mat(C)
ans =
1 1
2 2
3 3
I had the same error, I just commented out the lines in cell2mat that return the error and everything work fine to me.
lines to comment out in cell2mat (51:53): (you can find them using dbstop if error)
if cisobj || ciscell error(message('MATLAB:cell2mat:UnsupportedCellContent')); end
I don´t think it is a good idea to change matlab functions, and I am pretty shameful of my solution myself, but it works.