For the past several days I've been hampered by the fact that the keyboard shortcut SHIFT+TAB wasn't working in IE.  This was driving me nuts!

I found that disabling the Windows Live Toolbar brought back the functionality (the only add-in besides Fiddler that I had installed).  Well, that was disconcerting as I enjoy having that toolbar present.  When I brought the toolbar back SHIFT+TAB would continue to work...that is, until I reopened the browser, then the problem was back.  I suspected it wasn't the 'toolbar' per se, or this would have been a more well known issue.  After a bit of deduction, I figured out that the Highlight Viewer button was the problem.  I removed the button (and restarted the browser for good measure) and my suspiscions were confirmed.

Is anyone else experiencing this issue?