I really wonder sometimes what the Yahoo Music engineers are doing over there. Are there any usability or QA teams? I'm a seconds away from canceling my membership, and suddenly Zune is looking more and more appealing because of my experiences. (On top of this, Yahoo is raising its rates in November ... a pretty bold move in the face of additional competition.)
So what's happening here? Well, before I start into that, let's just say that I haven't been too impressed with the quality of the app to this point ... script errors, playback errors, etc. Just lacking polish. So, I launch Yahoo only to find an update I must install. No biggie. I install the update. Only, I can no longer play any music. I load up a playlist, hit play, and am greeted by this dialog:

Hmmm. I'm not even trying to use "Boost", but whatever. So I click OK. Now, regardless of whether or not you click OK or the close button, a new browser window opens with a
help page. That's a minor issue. Apparently the most common problem is a 3rd party component, except, I don't have the one they mentioned installed. Let's remember, though, that all I did was install the update to break this, so at present, Yahoo is to blame for breaking their own app.
While that new window is open, the player is still unable to play the song (despite what the dialog says), so, it attempts to move on to the next song in the playlist. Dialog opens ... repeat by closing the dialog, new browser window, repeat again. There's no way out of this vicious cycle except to use Task Manager and shut it down. For long playlists (like mine), this is a huge usability issue and bad enough to be a bug.
This isn't the first time I've seen this, though, in the Yahoo Music Engine. If for some reason a song cannot play (e.g. a DRM issue), a pop up would tell you to reinstall the license file. And it would do this for every song in your playlist (if you lose one license file, you've probably lost them all for subscription music). Once again, Task Manager.
At the bottom of the help page is a link to contact Customer Care. I filled out the required information and attempt to submit. Only, I can't submit. You cannot contact customer care unless you agree to install a Yahoo ActiveX control for diagnosing the problem:

Um, no thanks. Anyway, not that I believe Zune will be the savior to all of the world's music problems, but a homogenous solution with half way decent software sounds pretty wonderful right now.