Windows XP SP3
Western Digital Passport Drive P/N WDPAAA5000ABL-00
After writing a very large file to my Passport drive, I try to "Stop" it by selecting the "Safely Remove Hardware" icon in the Windows tray, left-click, and then selecting the drive letters. After a long wait, I get an error popup that says: "the device 'Generic volume' cannot be stopped right now. Try stopping the device again later."
This happens whether my anti-virus application (AVG 2014) is enabled or disabled. The Applications tab for Windows Task Manager shows no applications that would be reading or writing the drive.