Sorry for the delay. I've just checked this on my end and we are actually using downloadmanager on this site (schlix.com). I've tested this with both PHP5.6 as well as PHP7 and cannot reproduce the error. Also you must configure the files to use the proper extension from "Configure". If the extension of the file is not registered, it will interpret it as a folder, which may be the case on your end.
Let me know if it's still not working even after you've changed the approved extension under "Configure" menu from the backend.
i did but problem still there.
so something its change becasue now file its stored to: web/main/data/private/downloads and it's right there but the link still to point to the same place: mywebsite.org/downloadmanager/files
i fill also something wrog coz can see an ' ) ' check the screenshot in attacment please.