Microspft has addessed this problem in its KB article Q324756: „You may not be able to install multiple Universal Serial Bus (USB) scanners in Windows XP and use them simultaneously. For example, when you attach two scanners to the Universal Serial Bus (USB) ports of your Windows XP-based computer, the first scanner that you connect is detected correctly; however, when you connect the second scanner, you may experience one of the following behaviors: The second scanner is listed in Device Manager as "Unknown Device". You receive the following error message (it is displayed next to the scanner in Device Manager): Windows cannot load the device driver for this hardware because a previous instance of the device driver is still in memory. (Code 38) This behavior occurs because the Usbscan.sys driver cannot be used simultaneously by more than one scanner. To work around this issue, connect and use one scanner at a time. To use the second scanner, disconnect the first scanner from the USB port, restart the computer, and then connect the second scanner. To use the first scanner, disconnect the second scanner from the USB port, restart the computer, and then connect the first scanner.“ Quote from Microsoft Article ID 324756 July 14, 2002