CS4 Space bar doesn't work to reposition a marquee

Help! I am drawing a marquee around an image and trying to reposition the marquee using the space bar on the fly, but the space bar function for this is suddenly disabled. I am using Photoshop CS4 for the first time on a new iMac (though I have used Photoshop for years on another Mac) and I don't know what could disable this functionality. The space bar toggle for the hand tool still works when using another tool. Any ideas? This is sooo frustrating and strange.

Have you tried the arrow keys?

This is from the CS4 Help file, so it hasn't changed:

To reposition a rectangle or elliptical marquee, first drag to create the selection border, keeping the mouse button depressed. Then hold down the spacebar and continue to drag. Release the spacebar, but keep the mouse button depressed, if you need to continue adjusting the selection border.

Your Photoshop preferences may be corrupted. Try trashing them.

<http://www.adobe.com/go/kb405012>

Make sure that your keyboard shortcuts are set so that Spotlight isn't activated with spacebar. You now have to remove or reassign most of the OS shortcuts to get Photoshop to behave properly.

Make sure that your keyboard shortcuts are set so that Spotlight isn't activated with spacebar. You now have to remove or reassign most of the OS shortcuts to get Photoshop to behave properly.

I found that on my system (MacBook Pro, OS 10.5.6) that the Spotlight shortcut is Command-Space and even if I were to press this and make Spotlight appear, I'm still able to reposition the marquee as normal.