When I double click I get the bizarre message, "you are about to start playback, do you want to clear the song previously, added up to Next?"

I get this message all the time, anyone know why? Thanks.

You don't say exactly on what you are double-clicking, but the message seems to indicate you are clicking on a music track or album. This is normal behavior for iTunes.

Maybe you didn't realize it, but you had an "Up Next" list filled with music. You can see this list icon (looks like 3 numbered lines) to the right of the "what's playing" box at the top of the iTunes window. If you interrupt this list by double-clicking on another song or album, you will get the message you saw.

Thanks Ira, never noticed those bars. Now it's not acting up, but when it does, what do I do to get rid of the message?

When I get that message there is an option to "Cancel". Click that and the message goes away and nothing changes.

But don't forget to be aware of what causes that message in the first place (see my original post above).

That's Ira, don't remember seeing cancel but will keep an eye out.

What causes it? I don't knowingly make a list. I do have playlist, but I've never seen this happen in last ten years.