When setup DefaultFileScope=App, Asset,Private receive Error 1101
When setup DefaultFileScope=Legacy or Shared Picture is received but Canvas is not present:
you can test the fix on the test server http://ai2-test.appinventor.mit.edu/
you will have to download the companion app of the test server to be able to test...
EDIT:
according to your screenshot, you like to download to the shared storage /Download... in this case you should set the Default FileScope to Shared...
alternatively if you don't want to share the downloaded image to other apps, you can set the Default FileScope to App and download to the ASD - application specific directory...