I have the same problem, the issue you are having is that your router doens't know how to route from the inside-out and back in again..nor should it.
What I do to get around this is add the FQDN to my /etc/hosts file pointing it at the local address of the server in question, it's a bit bodgy because really I should be running DNS (which if set up properly would get around all of this)
So for example my hosts file currently looks like
10.255.0.4 noisy 10.255.0.4 digimatic.plus.com 10.255.0.10 archie.clientaddress.com
Where noisy is my music server, digimatic.plus.com is the outside domain that resolves to my external IP address (and therefore the external name of my music server's web interface) and archie.clientaddress.com is a web server I am currently setting up for a client.
noisy is sort of redundant but it's quicker to type for ssh access etc so I tend to use it internally for access to the music server.
You may notice the slightly unusual address range...This is a side effect of dealing with lots of clients MS VPN's. In order for them to work properly I have to have a private address subnet that is different to everyone else.