As someone else said, it is very important to remember to "finalise" the disc, don't leave it open.
Watch for folders - some older MP3 players don't like too many folders (I had one in a Toyota that would only play stuff in the first 5 folders)
Watch out for a maximum number of files in a folder (including the root of the disc) - one player I had many years ago wouldn't play anything after the 128th file...
If your CD burner software is not working for you (or too complicated) - if you go over to www.ninite.com, you can get CDBurnerXP - very simple, straightforward and free! (and it works on Windows 10, despite the name)