I too am seeing this problem on my Perfection 1640SU. Pressing the acquire preview gives the message "Failed to start scanner: Operation not supported".
This on Debian testing. Now on the Advanced Options window, there is an Autofocus button. I have deactivated it. I am pretty certain that this model has no autofocus mechanism. There is also a Focus position bar. Again, I don't think this model has any way to implement that. So I suspect that the "Operation not supported" is to adjust the focus. The old xsane (I probably mean the epson backend) just showed two settings: "Focus on glass" or "Focus on film". That is from memory, but something close to that. SO perhaps this old model had just a binary switch for two focus positions, and the epson backend has been broken by assuming that this model has more focus facilities. So far this is pure speculation on my part. ael
