There is little square in the lower corner was created automatically when the curve was drawn. Now, I try to remove this square so when apply edge smoothing will not interrupt the model. What I did, removed the square and then found that the entire curved face was removed. Finally, i placed a straight line to connect both edges of the previous curve, but still the gap is not completely filled. I do believe that might be a non-coplanner geometry is taking place, but no idea how to fix this little problem. I look forward for your help and support and explanation of how to control this scenario in the future.
Images and model is attached with the message.