matlab dataset error displaying

Hi: I have matlab 7.6 and I work under PLS toolbox. I want to create and open existing datasets but it gives me the following error:

??? Reference to non-existent field 'nobs'.

Error in ==> dataset.isempty at 11 t = (a.nobs == 0) (a.nvars == 0);

Error in ==> editds>setvarname at 3248 if ~isempty(data) & ~isempty(data.moddate) & (isempty(moddate) | any(moddate~=data.moddate));

Error in ==> editds at 52 setvarname(fig,inputname(1));

Error in ==> dataset.openvar at 6 h = editds(varargin{2}); %create editor

Please any help for me? thanks in advance