Here's my situation:

I've got a proxy/firewall/dns machine running nat and a portmapper.
All local adresses are protected by nat. Including the local addres from our proxy. (so the proxy uses it's own nat to connect to the world)
I'm using the portmapper to map incoming web request to our web machine, which's got an addres in our local network.
When i try to open the site from outside our network (ie from the net) everything works great, but from inside our network (intranet) we can't seem to connect to our 'outside' url. (when i use the inside ip / host addres it works fine though.) It does'nt matter if i set my browser to use the proxy or not.. (the request should be routed to a local addres by the portmapper so the firewall shouldn't hold the request).
I can connect to our DNS machine using nslookup, so the problem should not be in nameresolution

I can ping the url, and everything looks fine ..
Still i get an 'acces denied' when i try to open our site from the intranet using the proxy or 'not found' when i try to directly open the site.

Dunno if this is really a security problem .. (gues not)
But i'ts got something to do with our firewall ?

Where to search.. ?