Hi,
if url is like this:
http://dl.google.com/dl/appinventor/installers/<platform>/appinventor_setup_installer_v_<version>.<extension>
and not work, try to use this:
https://dl-ssl.google.com/dl/appinventor/installers/<platform>/appinventor_setup_installer_v_<version>.<extension>
Did my HOW TO help you?