I ran into the same error code (error -10049) today after relocating my computer and trying to host a MP mission.
The error led me to look at my network.cfg file (C:/Users/username/Saved Games/DCS/Config). The suspect "interface" line in that file contained the correct static IP I had previously assigned to my PC from my router. When I checked my router, it still showed that static mapping to my PC's MAC address. When I then did an "ip config" from the DOS prompt and saw the actual assigned IP address, I realized the router had assigned my PC a different, dynamic IP address. Then it hit me that my motherboard has two Ethernet ports (each with a different MAC, of course) and I had plugged the Ethernet cable into the "wrong" port.
Once I plugged into the other Ethernet port, everything worked fine again. Out of curiosity, I plugged the cable back into the "wrong" port and replaced the IP address in the network.cfg file to the one my router had dynamically assigned to that Ethernet port, and was also able to host a MP mission with no problem.
