Foreground to transparent in Gradient Map not working in Photoshop CS4 or 5

When I try to use a Gradient Map adjustment layer, and I click on the Foreground to transparent option, it simply appears as all black (or all white if the foreground color is white) rather than the gradient to transparent as it should appear.  I only get this behavior in the Gradient Map adjustment layer, not in the Gradient Tool.  I have tried resetting the default settings for this adjustment as well as the Photoshop settings in general with no success (including deleting the *.psp file).