In a multiplayer environment it's possible that a playlist does not seem to load and songs can't be played anymore. The host and some additional players may not see any error messages.
A reason for this could be as follows:
^ This has since been fixed in v1.4.0

- TTS only connects with the internet when a song is loaded for the first time. It will keep previously downloaded songs locally stored on your computer. That means those songs in your playlist will still keep working even if the URL becomes unreachable or otherwise invalid!

- When someone joins who has never downloaded the song, they try to connect to the URL for the song that is currently playing. They can't download the file (because the URL is invalid) and then the music player will fail for everyone. The host will see no error message. Only the person that joined will see an error message in the chat window saying: "AudioClip Error: Unsupported File Format!". This is very confusing, because the error message is wrong. The issue is that the URL became unreachable, so that person can't download the song.

This means that you need to check all the URLs in your playlist, for example in a web browser to see if they are still reachable. Then remove all unreachable URLs from the list and try again. The issue should then be fixed.

To simply copy all the URLs from your playlist, do the following:
- Start your game in single player
- In the Music Player Extension menu: make sure the U button is toggled to show urls
- Load the playlist you want to check
- Copy the text in the window on the right to a text editor like notepad. You can select the text with the mouse and press Ctrl+C to copy.
- Check all the urls in a web browser to see if they are still reachable.
- Edit your playlist in the Music Player Extension to remove all the songs with bad urls

Removing a song:
- In the Music Player Extension menu: Click Playlists -> Edit [my playlist]
- Click on the box that says 'Remove Song #...' in gray text
- Type a number (press Space to clear the number if needed)
- Click Remove song
- Repeat

In the mean time I'm working on improvements on error reporting so you can see a message in the text window on the right that will urge you to check URLs for validity. I will also look at ways to skip this song so that the rest of the playlist can still be played.

EDIT: This has since been fixed in v1.4.0