Seems like Cmodo is not friendly with NS2. I am not sure about the other anti virus and firewall programs but if you are having trouble, try turn off while playing ns2.
It worked for me after all the steps I did on above method.
1. Delete NS2
2. Delete all files in windows start -> type in run box -> %APPDATA%\Natural Selection 2 folder
3. Uninstall Steam
4. Search and delete all steam and natural selection fi…