xsane doesn't work with ScanPrisa 640U Acer/Benq/Vuego scanner - Failed to open device 'snapscan:libusb:007:003': Invalid argument.

This scanner worked for me in 10.04 Lucid, but has not worked subsequently in 10.10, 11.04, 11.10, or 12.04
Scanner details:
  Brand name: Acer
  Model name: ScanPrisa 640U
  Model number: 6698-AVF
  Mfg Date: April 2000

$ xsane
  [snapscan] Cannot open firmware file /usr/share/sane/snapscan/your-firmwarefile.bin.
  [snapscan] Edit the firmware file entry in snapscan.conf.

$ sane-find-scanner

  # sane-find-scanner will now attempt to detect your scanner. If the
  # result is different from what you expected, first make sure your
  # scanner is powered up and properly connected to your computer.

  # No SCSI scanners found. If you expected something different, make sure that
  # you have loaded a kernel SCSI driver for your SCSI adapter.

found USB scanner (vendor=0x04a5 [Color], product=0x2060 [ FlatbedScanner 13]) at libusb:007:004
  # Your USB scanner was (probably) detected. It may or may not be supported by
  # SANE. Try scanimage -L and read the backend's manpage.

$ scanimage -L
device `snapscan:libusb:007:004' is a Acer FlatbedScanner13 flatbed scanner

$ scanimage -d snapscan:libusb:007:004
[snapscan] Cannot open firmware file /usr/share/sane/snapscan/your-firmwarefile.bin.
[snapscan] Edit the firmware file entry in snapscan.conf.
scanimage: open of device snapscan:libusb:007:004 failed: Invalid argument

In /etc/sane.d/snapscan.conf
    ...
    # Benq/Acer/Vuego 640U
    usb 0x04a5 0x2060

$ lsusb | grep -i acer
Bus 007 Device 004: ID 04a5:2060 Acer Peripherals Inc. (now BenQ Corp.) Prisa 620U+/640U

I also downloaded and ran "VueScan" from hamrick.com and it reported "No scanners were found connected to your computer, and no raw scan files were found."

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: xsane 0.998-3ubuntu2
ProcVersionSignature: Ubuntu 3.2.0-25.40-generic 3.2.18
Uname: Linux 3.2.0-25-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.0.1-0ubuntu8
Architecture: amd64
Date: Sun Jun 24 09:26:18 2012
ExecutablePath: /usr/bin/xsane
SourcePackage: xsane
UpgradeStatus: Upgraded to precise on 2012-04-26 (59 days ago)
XsessionErrors:
 (nm-applet:1715): GdkPixbuf-CRITICAL **: gdk_pixbuf_scale_simple: assertion `dest_width > 0' failed
 (compiz:1672): GConf-CRITICAL **: gconf_client_add_dir: assertion `gconf_valid_key (dirname, NULL)' failed
 (gnome-settings-daemon:1393): GLib-CRITICAL **: g_variant_get_int32: assertion `g_variant_is_of_type (value, G_VARIANT_TYPE_INT32)' failed