Gives an error Emgu.CV.Util.CvException: OpenCV: !empty() how to fix it?

Question

OpenCV

can't fix error google says nothing...
Gives error Emgu.CV.Util.CvException: OpenCV: !empty() how to fix it?
when accessing a string:
var _Faces = _Cascade_Classifier.DetectMultiScale(_Next_Frame, 1.1, 4, new Size(_Current_Frame.Width / 8, _Current_Frame.Height / 8), new Size(200, 200));
Works on another PC!