Error message when download Wincc project from ES to OS

hello

I have single station Wincc project and I want to download the project from ingineer Station ES into operator  station OS for that:

-I make local ethernet network and I connect the two stations

- I integrate the project into step 7 and I specify the target OS path

- I add the windows user into SIMATIC HMI user

but when I put download to OS I got error message that

'"the data base doesn't exist or it is not valid" 

How can I solve this problem please?