TNet can only open ports if UPnP is accessible. If the router doesn't support it, or if there is no router, then the ports can't be opened. If the router doesn't support UPnP, you will need to forward ports manually. If there is no router, then you don't need to do anything. Since you mention that you turned off the firewall, it sounds like you don't need to worry about it.
The crashing was resolved with 3.0.2b. It wasn't a crash per say, just an uncaught exception that was only showing up on non-Windows platforms.