Better late than never. For Ubuntu 14.04
They just didn't finish the instructions, because I was getting the same error. After you complete the steps there, search for Remmina Remote Desktop Client, already installed with Ubuntu.
Click Create New> VNC Incoming Connection
port: 5901 you said
username: copy the username from the app on your phone
password, again, same password as what's on your phone.
Match the color depth and I suggest clicking to show remote cursor.
Click Connect and set to default settings if you'd like.
Restart your computer, open up Remmina again, select the remote desktop file we just made, click Open the conection in the top left and THEN click connect on androidVNC.
Hope that helps.
Cheers.