You need to forward certain ports in your router for DCC to work. By default, it's 1024-5000 but it's understandable you may not want to forward that many, so you can always specify a minimum of two ports (preferably in that range however) and set them in
ALT+O > Connect > Options > [Advanced].
This thread holds many suggestions, and has some links related to help with D-Link router setup. You may also like to use the Forum
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G'luck!
Regards,