"create sibling and layout" keyboard shortcut (Pro version)

[Rick Lavin]

Does anybody know this shortcut? In the menu, it looks like 
command-option-apostrophe or comma, but neither of these works, and nor 
does command-option-@, which has an apostrophe-like mark on it too. The 
other shortcuts do work, and the corresponding menu command works, too, 
so it doesn't seem to be any fundamental problem. Thanks for any help,
Rick