VueScan didn't find a scanner connected to your computer.
1) Make sure the scanner is plugged in and turned on before you run VueScan.
2) If you have a USB scanner, try a different USB cable and/or a different USB port.
3) If you have a WiFi scanner, make sure your firewall isn't blocking responses from the scanner.
4) If the scanner has a locking switch, make sure it's in the unlocked position.
5) Try turning your scanner off and back on.
6) If you have a USB scanner, use 'About This Mac' (in the Apple menu) and see if the scanner appears in the USB devices section.
Then exit VueScan and run it again.
If it still doesn't work, try installing the x64 version of VueScan from www.hamrick.com (scroll down the page a bit to find this).
The supported scanners list has more useful information about your scanner. Would you like to see this?