Error When Ejecting iPod After Sync

After syncing my Music Library to my iPod device, I clicked on the little "eject" symbol in the iTunes program window so that I could unplug my device. However, an error message popped up.

Error Box Title: mfac.exe - No Disk

Error Box Text: There is no disk in the drive. Please insert a disk into drive D:.

After clicking either "Cancel," "Try Again," or "Continue" the same error box pops up a second time. After I make a second selection (and I tried all possible combinations of those three options), the window disappears and a new error appears.

2nd Error Box Title: iTunes

2nd Error Box Text: The iPod <my device name> cannot be ejected because it contains files that are in use by another application.

The only selection in this box is "Okay."

Needless to say, the iPod does not eject, and now I can't remove it from my computer. I tried closing and reopening iTunes, and then restarting my whole computer, but the problem persists. I have never used my iPod to transfer any files other than a synced music library, or enabled the "use as removable storage" option.

I am using a Windows 8.1 and iTunes version 12.1.2.27 64-bit. My device is an iPod Classic with software version 2.0.1.

Thank you.