If you have any Windows Explorer windows open browsing your iPod, TouchCopy will not be able to eject your iPod. Please close down any other such windows or applications accessing your iPod and then try to ejecting your iPod.
Also, closing down TouchCopy will automatically eject your iPod.
Please also ensure that you're using the latest version of TouchCopy by using the updates checker in TouchCopy Options.
To manually eject your iPod once all applications using your iPod have been closed (including TouchCopy):
Open My Computer or Computer in Windows Explorer. Right click on your iPod drive icon and select "Eject" from the pop-up menu.
Drag your iPod icon on the desktop onto the trash icon in the dock.