(I'm Thai sorry for my bad english)
I try to change browser to preview but it still have a problem
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Something might be using your 50000 port, if you don't want to risk breaking anything in your computer configuration, try changing the preference to 50001 or any 500## you like, see whether that helps.
Preview over LAN doesn't work with free edition.
I presume free edition can still preview over localhost. Check your firewall? Check your hosts file that you didn't change something there.