Why is Reading Pane toggle button no longer available?

[tunghoy]

On my laptop, I have Outlook 2007 build 12.0.4518.1014. I placed a button on
the toolbar that toggles the Reading Pane on and off (dragged the button from
the Customize/Commands/View dialog).

But in Outlook on my workstation, running a slightly newer version of
12.00.6316.5000, this command is no longer available. Not only that, but when
I go back onto the laptop, that button isn't available anymore, either!

I am the only person who uses either of these machines, and I have not
installed any 3rd-party tools for Outlook or written any macros.

Any ideas what's going on? Is Microsoft randomly disabling features?

 

[tunghoy]

Well frack me, the tool is under the Advanced category, in case anyone else
is interested. I swear I checked all the categories over and over. Maybe I
need new glasses.