A problem I recently encountered was that I couldn't adjust the virtual server settings via SharePoint Central Admin of a virtual server using SSL (https). After some googling it turned out t o be a bug (which apperantly isn't fixed in SP 2 of WSS). So I'll always got the same error:
The server instance specified was not found. Please specify the server's address and port.
The solution/workaround is pretty simple.
Lets say the url looks like this: http://mycentraladminurl:007/SPSecuritySettings.aspx?VirtualServer=https%3a%2f%2fmyvirtualserver.
Notice the https in the VirtualServer parameter. Just change this to http (drop the s) and everything will work.
And by the way here is the link to WSS SP2