Well, I got my Epson Stylus NX420 scanner working. Not to my complete satisfaction, but it works. Here's what I did.
First, I opened up the terminal and typed: sudo apt-get install libsane-dev
Then I downloaded the file http://launchpadlibrarian.net/14664165/45-libsane.rules
and pasted it in etc/udev/rules.d/ and then edited it by adding the line
# Epson Stylus NX420
SYSFS(idVendor)=="0x04b8", SYSFS(idProduct)=="0x0864", MODE="664", GROUP="scanner"
I tried pressing the button "Scan" on the NX420 itself, and the machine still said "Communication error. Check the connection". So I rebooted. Once I logged back in, and pressed the Scan button on the machine, it again said error.
However, when I opened up XSane Image Scanner, and I clicked the scan button on the screen, it worked! I don't know if a reboot is mandatory, but before you do, try using the XSane interface to scan before rebooting.
It'd be nice if I could press the button on the scanner itself and make it work. Any ideas?
And thanks for this thread. It helped!