Home Forums Mac Software Mac Operating Systems can't eject external drive

I formatted a USB flash drive with Disk Utility (Mac OS extended, journaled) and quit DU. I then copied two files to the drive. When I tried to unmount the drive, I got a message that a program was using it and I was given the option to Force Eject (with a warning that data might be lost) or cancel. I opted to cancel and then restarted the computer.

After restarting, I was able to eject the drive and physically unplug it. (Yes, I could have shut down and then unplugged the drive but I opted for a restart.) I know that I could look in Activity Monitor to see which program was using the drive (which shouldn't have been the case) but I don't know what to look for. BTW, the same thing happened awhile ago with a HDD in a dock.

What should AM say? I could have quit the process from there. I looked but couldn't find anything that seemed relevant.

MODS: I wasn't sure if I should post this here or in the Peripherals forum. Feel free to move it.