"Sorry, the player does not support this type of audio file"

Just taking a wild guess but it sounds like when you were renaming those files you didn't retain the file type suffix (eg. SongName.mp3). Try renaming a couple of those songs you changed before so they have their .mp3 identifiers back (or .aac or .ogg or whatever file types you save your songs as) and see if your music player can play then again.

 

Just be more careful when you're renaming files. Whenever you want to rename your audio files just edit the part to the left of the period and be sure to leave that file identifier part to the right as is -- a file named originally named 'FileName.mp3' would be 'Changed.mp3' after you edited it.

 

Perhaps contact that website and ask if renaming a ripped audio file causes known issues?

We can't really help as converting YT content for offline use is against YouTube's T&C, as well as breaching the original owner's copyright.

 

A lot of Youtube content is protected by patents so there are DRM restrictions. Some musical artists simply don't want their fan-base to be able to pirate their efforts for free. Some musicians just put their work up on Youtube so they get more exposure to the public so it sounds like you've got a mix of songs of falling into both categories. While there are ways to bypass DRM-protected songs that's something you need to look into yourself, this forum does not support illegally pirating songs.

 

There are a number of online sources for freely downloadable content, along with pay-for services like Amazon, Apple iTunes, and Google Play.
http://www.hongkiat.com/blog/creative-common-music-download/

Some songs are rare, hard to find, or available only on vinyl or CDs. Sometimes it just comes down to buying the record or CD and ripping it yourself.