Why do I receive "Cell contents reference from a non-cell array object." error?

Why do I receive "Cell contents reference from a non-cell array object." error when I execute this code?

handles.num=1;
handles.den=2;
handles.num{:}

Cell contents reference from a non-cell array object.

Answer 1

[Jorrit]

Try round brackets instead handles.num(:). These ones {} are used for cells.