The two interfaces are on the same network or on different ones?
On which one is the server's default gateway?
Where are you connecting from?
RDP normally listens on all the server's IP addresses, so you should be able to connect to any of them, unless some firewall (including the server's one) if blocking you.
But if all of the following is true, you'll have a so-called "split routing" problem, and you won't be able to connect:
- The server has IP address A on network A and IP address B on network B
- The server's default gateway is on network A
- You're trying to connect to IP address B
- You are not directly connected to network B
In this scenario, your packets will reach the server on IP address B, but it will send its replies via IP address A to its default gateway, because your address is not located on any network it can directly reach; so those packets can, and probably will, be dropped by some router in the middle, which will not like them (and for quite a good reason).
A possible solution could be setting a static route on the server, in order to tell it to reach the network your client sits in via the same router the connection is coming through.
Let's say you have the following scenario:
Network A: 192.168.1.0/24
Network B: 192.168.2.0/24
Network C: 10.1.2.0/24
A default gateway for network A with IP address 192.168.1.1
A router between network B and network C with two IP address: 192.168.2.1 and 10.1.2.1
Server's IP on network A: 192.168.1.10
Server's IP on network B: 192.168.2.10
Server's default gateway: 192.168.1.1
Your client's IP on network C: 10.1.2.3
Your client's default gateway: 10.1.2.1
In this scenario, your connection will go through the router which sits between network B and network C, but the server will send its replies to network A's gateway (hence the split routing problem).
You could add a static route to the server to tell it to reach Network C via the other router:
ROUTE ADD -p 10.1.2.0 MASK 255.255.255.0 192.168.2.1
If this is your scenario, the static route solution should work fine.