I think this happens when you load map which you dont have in W3 map folder.
after u load map, try pub it some simple gn like: .gopriv 1and then dont serach it in custom games list, just try typing 1 and enter it.
You should try entering/searching when you get a whisper from the bot Creating public game [xxx] started by [xxxx].Because it takes some time to create it and then you might need to wait few seconds till it appear.