The exception is caused by disabled Download Manager. And there is no way to activate/deactivate Download Manager directly, since it's system application and we don't have access to it.
Only alternative way is redirect user to settings of Download Manager Application.
try {
//Open the specific App Info page:
Intent intent = new Intent(android.provider.Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
intent.setData(Uri.parse("package:" + "com.android.providers.downloads"));
startActivity(intent);
} catch ( ActivityNotFoundException e ) {
e.printStackTrace();
//Open the generic Apps page:
Intent intent = new Intent(android.provider.Settings.ACTION_MANAGE_APPLICATIONS_SETTINGS);
startActivity(intent);
}