or leads to where I can go for more clues on how to get rid
of it?

The sandbox is simply a place on your hard drive reserved for Flash to
operate. If you are having a violation, it is because something is
attempting to get outside of that reserved space; it could be rather benign
put it also could become a major security problem and future headache.

My guess is that because it's happening while going to myYahoo, it is
related to that site and not the other site, even though the message
appeared to coincide with the latter. I'm thinking the error would also
likely be that the code in Yahoo is calling something that had been
downloaded previously, but Flash is not allowing this to happen for some
reason. I would attempt to clean the hard drive up. First, I would
re-install the latest version of Flash. Next, I would go to the
Tools/Internet Options menu in Explorer. While there, click the Delete
Files button, check the Delete all offline content box and click OK (I tend
to think that most people are better off clicking the Delete Cookies and
Clear History buttons also, but you may not want to do this if you frequent
sites where you might have to re-enter information). Next, I would also
find any folders on my hard drive labeled Temp or Temporary Internet Files
and delete the contents in them.

Then, of course, the standard tech-support line -- restart your machine.

If you are still having problems, I ran across a site that supposedly offers
software that allows you to turn Flash on and off...this might help, but I
have never used it. http://www.flashswitch.com/ I think it's free
software.

Good Luck
Tim