With the recent Ubuntu 21.10 upgrade, I experienced an error when starting iscan that I used to run my outdated old Epson legacy flatbed scanner. Because, hey, old hardware.
Running ‘sane-find-scanner' would cause a 'could not fetch string descriptor: Pipe error' error.
The iscan application would not start, whereas xsane worked perfectly.
The solution seems to be a bug in the system upgrade whereas symbolic links need to be added by the user themselves.
Directly from [https://forums.linuxmint.com/viewtopic.php?t=298418] as posted by user patanjali :
The crucial difference was that the newer system was not looking in /usr/lib/sane, but the older system was. Maybe this is a bug, but in any case the problem was solved simply by adding symbolic links to the /usr/lib/x86_64-linux-gnu/sane/ directory. (I like using the -v flag to see whether the system did what was expected):
Code (what I did was run the command highlighted blue as root):
root@ganaka:~# ln -sv /usr/lib/sane/* /usr/lib/x86_64-linux-gnu/sane/ '/usr/lib/x86_64-linux-gnu/sane/libsane-epkowa.la' -> '/usr/lib/sane/libsane-epkowa.la' '/usr/lib/x86_64-linux-gnu/sane/libsane-epkowa.so.1' -> '/usr/lib/sane/libsane-epkowa.so.1' '/usr/lib/x86_64-linux-gnu/sane/libsane-epkowa.so.1.0.15' -> '/usr/lib/sane/libsane-epkowa.so.1.0.15'
And with that, iscan was back.
Disclaimer – there are zero guarantee this works elsewhere ; ) there are zero guarantees anyways.