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       group and a saned user.  If you follow this example, please
       make sure that the access permissions on the special device are
       set such that saned can access the scanner (the program
       generally needs read and write access to scanner devices)." :-)

> and the error message is misleading.

That's true. Well, at least it's not clear, beacuse SANE_STATUS_INVAL
means "some other error occured".

> It only des it when the permissions on /dev/usb/scanner0 are wrong.

So I assume it's a plustek problem even if I don't see any obvious bug.

> [dll] load: dlopen()ing `/usr/lib/sane/libsane-net.so.1'
> [dll] init: initializing backend `net'
> [dll] init: backend `net' is version 1.0.10
> Segmentation fault (core dumped)

Looks like it happens in sane_open. Please Try setting "export
SANE_DEBUG_PLUSTEK=255" also

> >Could you try to run saned in gdb directly? Maybe that gives more
> >information.
> 
> I'm not a gdb expert.  How do I do this?

gdb saned
run -d128

Now start scanimage. When saned crahes, run bt to show the backtrace.

Bye,
  Henning