Can not add Music to Slideshow

This is the second time posting this question.  I have seen other questions regarding the same thing, but no answers.

Just upgraded to Lightroom Classic CC and unable to create a Slideshow.

Trying to add music to my slideshow and keep getting the message that the Music is Not Formed.  I have use the music file before.

Can someone help me, I use the slideshows for my business.  I have been waiting forever to find someone who can help me.

I am using macOS Sierra Version 10.12.6