Incorrect version of Natural Selection, or corrupt client.dll (the file which tells the server what version of NS you're running).
Backup any configuration files (default location at C:\Program Files\Steam\steamapps\<Steam Account Name>\hl\ns\config.cfg), close Steam (Right click in the system tray and click on Exit). Then uninstall Natural Selection, via the Add/Remove Programs panel in Control Panel.
In the meantime, download an up to date copy of Natural Selection from <a href="http://www.unknownworlds.com/ns/?action=files" target="_blank">one of the offical mirrors</a>. Install it when it's finished downloading, all default settings are correct (it pulls the correct Steam location from your registry), finish installing. If you've backed up your configuration files, then they go back into C:\Program Files\Steam\steamapps\<Steam Account Name>\hl\ns\config.cfg (Make sure it's called config.cfg).
Re-open Steam, click on My Games, then open up the new, up to date, installation of NS.
Have fun <img src="style_emoticons/<#EMO_DIR#>/smile-fix.gif" style="vertical-align:middle" emoid=":)" border="0" alt="smile-fix.gif" />
Comments
Backup any configuration files (default location at C:\Program Files\Steam\steamapps\<Steam Account Name>\hl\ns\config.cfg), close Steam (Right click in the system tray and click on Exit). Then uninstall Natural Selection, via the Add/Remove Programs panel in Control Panel.
In the meantime, download an up to date copy of Natural Selection from <a href="http://www.unknownworlds.com/ns/?action=files" target="_blank">one of the offical mirrors</a>.
Install it when it's finished downloading, all default settings are correct (it pulls the correct Steam location from your registry), finish installing. If you've backed up your configuration files, then they go back into C:\Program Files\Steam\steamapps\<Steam Account Name>\hl\ns\config.cfg (Make sure it's called config.cfg).
Re-open Steam, click on My Games, then open up the new, up to date, installation of NS.
Have fun <img src="style_emoticons/<#EMO_DIR#>/smile-fix.gif" style="vertical-align:middle" emoid=":)" border="0" alt="smile-fix.gif" />