ASUS AiCloud is a very useful and powerful feature of its routers if you would like to access the shared folders of networked computers anywhere there is an internet connection. However, there is one glitch that may cause problems accessing the computer even though it is shown on the list of devices. User ID and password will keep pop up even though correct information is entered. The cause and the solution are not well documented anywhere.
If you are using Windows 10, there has been a security patch which has turned off SMB1 network sharing. You might need to re-enable this. Go to Control Panel, Programs, Turn Windows Features on or off and turn on both options under SMB1.0/CFIS File Sharing Support. You will need to restart after this. And that should resolve the access problem.