My Light Controls window has disappeared. when the Pose room is open.  In the Materials room, the "Light Controls" title and controls are there, but they are nowhere to be seen in the Pose room.

Yes, I've toggled the "Light Controls", so please don't offer that answer-- off and on, off and on, several times.  No LIght Controls.  I'm not a noob-- I just can't find my light controls for some reason.  I've tried reseting to the factory state-- no luck.  I have no idea whay they are missing now either.  Is it something I've done?

Has anyone else ever had this problem?

Have you tried deleting the prefs file yet?  This file (PoserUIPrefs_1024x768.xml or
similar name with other numbers) contains the positions for the light ball. 

You could edit the file to see if the X and Y for the light ball are way off, like this:

    <WidgetPrefs widget="eP4LightBall"  left="2053"  top="2089"  bottom="168"  right="132"  collapsed="2"  rect.left="53"  rect.top="89"  rect.right="132"  rect.bottom="168" />

but it's probably easier to delete the file and let Poser rebuild it with default values.

Typically this file will be in Documents and Settings / .... / Application Data / Poser 7.

Thank you Ockham, your name strikes true.  The simplest solution was the best one.

I owe you one...

It usually works if you set back to Factory default settings, then restart Poser and set back to User settings .