'Generic Volume' error

I have a 250 usb powered zip drive. i remove it by clicking safely remove hardware on the bottom right screen and then i chose the drive and press stop. After pressing stop it comes with an error saying the drive generic volume cannot be stopped because a program is still accessing it. Problem is that no program is running. What might be the problem with this?

 

There's no problem per se. I occasionally experience the same hiccup with my USB jump drive. It's just probably a process running the background that hasn't finished what it's doing after you've unplugged the drive.

On a side note, a slightly faster way to unplug the device would be to LEFT-click on the icon in your system tray rather than right-clicking. A left-click will give you a pop-up box which you can click on to immediately terminate the device and remove it safely.