There's already another program using port 23073.
This might be another Soldat client still running in the background though, try using the task manager to close all soldatserver.exe and Soldat.exe programs. It might also be that there's another program that uses port 23073, though this is going to be harder to find out.
Let me know if closing down all soldatserver.exe and Soldat.exe files worked or not, if not then I'll look up how you can see what program is using 23073.
Grtz, DePhille