If your router has UPnP abilities, make sure UPnP is enabled within the router. Otherwise if it doesn't support UPnP, you would be better to manually forward a port. See Connection problems? Check here first! for instructions about this.

A quick check is, do this test: Bug Report instructions & sample image Is the result True/False?
If false, then either your firewall or router is not properly configured.

Also, go to LW's menu, Tools>Options>View>Popups>Revert to Defaults & tick the option & press apply button. This will stop LW automatically deciding a file is corrupt, & will instead ask you whether to continue with it.