Cisco Firewall :: ASA 5520 / 2911 - TCP Reset-O Message

Here's the current scenario:
 
[LAN] <---> ASA 5520 <---> Cisco 2911 <---> [Internet] <---> Server A
                         |
                         |
                     [DMZ]
 
Whenever I access a website running in "server A" (only HTTP traffic) everything works fine. The problem is that when I try to access a different service on the same server but listening on port 2000/tcp I get the TCP Reset-O message on the ASA and the workstation's browser says that "Internet Explorer cannot display the webpage".
 
A weird thing: if I access this service from a machine on the DMZ, it works fine. From the LAN (Inside) it does not work. The main difference is that from the LAN to OUTSIDE the ASA does NAT. From the DMZ to OUTSIDE it's just routed. I did another test from the LAN and the captured traffic is attached. I've been messing around with protocol inspects and firewall + NAT rules on the ASA but no luck at all.