Comment 17 for bug 844582

As you have noted, the 001:005 refers to the usb device. However this can change between boots. Did you reboot between the gscan2pdf/scanimage and epson sessions?

As you can reproduce this from the commandline with scanimage, I am transferring this bug to sane-backends, as the bug must be in the epson/epkowa backend in SANE.

"Invalid argument", is simply the error code that libsane returns. Unfortunately, it does not provide any more information that that by default.

However, you can run scanimage with debugging turned on. I would ask on the SANE mailing list for more help.