Firewall/NAT

Hello
There is a RDP Server in my LAN . I use RDP from LAN and also from WAN. It works fine but only without captive portal.
If i switch on the captive portal (because of all other users in my LAN) the Server can not answer now. As long as i have html connection at the server it works fine.
How do i make a hole in the captive portal rules to get access?

rgs
frank