Hi Alexey,
I was just editing, no classification. I use the basic module of photoscan 1.3.
I open the project again and I noticed that when I move the arrow cursor on the model window on the console pane appear the message ERROR : null file repeatedly during cursor movement. When the cursor is outside the model window the printing error: number is stopped.
In the mean time I reproduced the dense point cloud with the same sparse point cloud and everything is ok.
I attach the console pane output.
Thank you for your answer.