Sorry, your image attachment didn't work, so I can't see the error.
==>Hi Bruce,I have re-edit the link of image attachment. Also you can see that correct image with link "http://i3.6.cn/cvbnm/fd/8d/21/e01977eb9f32990e8d9f8253df9b5ad7.jpg".
When you say 'action menu', do you mean the normal DNN site menu? Does it not show up, or does clicking on the links not work?
==>Yes,It's normal DNN module menu and It does not show up.
Also, is there only one child portal in the installation, or are there others. If there are other child portals, are they also affected with the problem, or do they work OK?
==>All of child portal are also affected with the problem once the url master has been enabled and you are trying to use the alias.