How can I uncheck "Enable disk use" in iTunes for my iPod? The option is grayed out, and permanently checked.

When I plug in my iPod Nano (6th generation) and launch iTunes, the device appears in the sidebar as normal, but the option to check or uncheck "Enable Disk use" in the Summary pane for the iPod is grayed out. Currently, the box is checked, so "Enable disk use " is turned on -- but what I want to do is UNcheck it and turn it off.

But nothing I've tried so far has successfully ungrayed the "Enable disk use" box. Help!

Question: How can I ungrey the "Enable disk use" option in my iPod's Summary panel in iTunes, allowing me to uncheck it?

Alternately, is there any other way to turn off "Enable disk use," using some esoteric workaround? Thanks!