While trying to connect to an AIX box, and start dbca, I got the following error
Xlib: connection to "192.168.0.100:0.0" refused by server Xlib: No protocol specified
This is an issue with Xming security. I changed the shortcut on my windows desktop to:
"C:\Program Files (x86)\Xming\Xming.exe" :2 -clipboard -multiwindow -ac
I was immediately able to fire up dbca.
the -ac option disable access control restrictions, so you should never do this over a public network, it could open up a massive hole in your computer and allow anyone to connect.