You could get that error under a couple of different circumstances:
- the helpdlg somehow gets closed before uiwait() gets control, in which case uiwait() would be passed a handle to a deleted figure
- or perhaps you have some non-standard helpdlg() function that is not returning the handle to a figure
Experiment with
h = helpdlg('Examine the figures, then click OK to finish.');
class(h)
if ishghandle(h); uiwait(h); end
This will allow you to examine what is being returned by helpdlg. class() will stil show 'matlab.ui.Figure' for deleted figures, but ishghandle() is false for deleted figures
