I also have the problem where simple-scan craches after clicking on "scan" button. Sometimes it crahes in the middle of a scanning process.

I am running Debian 7.2 
simple-scan: 3.4.2

Here is a report about similar problem on Debians bugtracker: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=680601 

Here is some output I get when running simple-scan with gdb:

 -> gdb simple-scan
GNU gdb (GDB) 7.4.1-debian
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/bin/simple-scan...(no debugging symbols found)...done.
(gdb) run
Starting program: /usr/bin/simple-scan 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fffeff00700 (LWP 7201)]
[New Thread 0x7fffeebd4700 (LWP 7202)]
[New Thread 0x7fffed25f700 (LWP 7203)]
[New Thread 0x7fffd77b7700 (LWP 7204)]
WARNING: gnome-keyring:: couldn't connect to: /home/fredrik/.cache/keyring-Sz0LZe/pkcs11: Filen eller katalogen finns inte
[Thread 0x7fffed25f700 (LWP 7203) exited]
[Thread 0x7fffd77b7700 (LWP 7204) exited]
[Thread 0x7fffeff00700 (LWP 7201) exited]
[Thread 0x7ffff7fd2920 (LWP 7198) exited]
[Inferior 1 (process 7198) exited normally]
(gdb) run
Starting program: /usr/bin/simple-scan 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fffeff00700 (LWP 7206)]
[New Thread 0x7fffeebd4700 (LWP 7207)]
[New Thread 0x7fffed274700 (LWP 7208)]
[New Thread 0x7fffd3779700 (LWP 7209)]
WARNING: gnome-keyring:: couldn't connect to: /home/fredrik/.cache/keyring-Sz0LZe/pkcs11: Filen eller katalogen finns inte
[Thread 0x7fffed274700 (LWP 7208) exited]
[Thread 0x7fffd3779700 (LWP 7209) exited]
[Thread 0x7fffeebd4700 (LWP 7207) exited]
[Thread 0x7ffff7fd2920 (LWP 7205) exited]
[Inferior 1 (process 7205) exited normally]
(gdb) run
Starting program: /usr/bin/simple-scan 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fffeff00700 (LWP 7268)]
[New Thread 0x7fffeebd4700 (LWP 7269)]
[New Thread 0x7fffed25f700 (LWP 7270)]
[New Thread 0x7fffd377c700 (LWP 7271)]
WARNING: gnome-keyring:: couldn't connect to: /home/fredrik/.cache/keyring-Sz0LZe/pkcs11: Filen eller katalogen finns inte
[New Thread 0x7fffcff7d700 (LWP 7273)]
[Thread 0x7fffcff7d700 (LWP 7273) exited]

** (simple-scan:7267): WARNING **: scanner.vala:977: Unable to disable compression, please file a bug
[New Thread 0x7fffcff7d700 (LWP 7274)]
[Thread 0x7fffcff7d700 (LWP 7274) exited]
[New Thread 0x7fffcff7d700 (LWP 7275)]
[Thread 0x7fffcff7d700 (LWP 7275) exited]
[New Thread 0x7fffcf77c700 (LWP 7276)]
[Thread 0x7fffcf77c700 (LWP 7276) exited]

(simple-scan:7267): GLib-GObject-WARNING **: instance of invalid non-instantiatable type `(null)'

(simple-scan:7267): GLib-GObject-CRITICAL **: g_signal_emit_by_name: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed

** (simple-scan:7267): WARNING **: scanner.vala:977: Unable to disable compression, please file a bug
[New Thread 0x7fffcd5e3700 (LWP 7332)]
[Thread 0x7fffcd5e3700 (LWP 7332) exited]

(simple-scan:7267): GLib-GObject-WARNING **: instance of invalid non-instantiatable type `(null)'

(simple-scan:7267): GLib-GObject-CRITICAL **: g_signal_emit_by_name: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed
[New Thread 0x7fffcd5e3700 (LWP 7333)]
[Thread 0x7fffcd5e3700 (LWP 7333) exited]
[New Thread 0x7fffcf77c700 (LWP 7334)]
[Thread 0x7fffcf77c700 (LWP 7334) exited]
[New Thread 0x7fffcd5e3700 (LWP 7335)]
[Thread 0x7fffcd5e3700 (LWP 7335) exited]
[New Thread 0x7fffcd5e3700 (LWP 7336)]
[Thread 0x7fffcd5e3700 (LWP 7336) exited]
[New Thread 0x7fffcd5e3700 (LWP 7337)]
[Thread 0x7fffcd5e3700 (LWP 7337) exited]
[New Thread 0x7fffcd5e3700 (LWP 7338)]
[Thread 0x7fffcd5e3700 (LWP 7338) exited]
[New Thread 0x7fffcd5e3700 (LWP 7339)]
[Thread 0x7fffcd5e3700 (LWP 7339) exited]
[New Thread 0x7fffcd5e3700 (LWP 7340)]
[Thread 0x7fffcd5e3700 (LWP 7340) exited]
[New Thread 0x7fffcd5e3700 (LWP 7341)]
[Thread 0x7fffcd5e3700 (LWP 7341) exited]
[New Thread 0x7fffcd5e3700 (LWP 7342)]
[Thread 0x7fffcd5e3700 (LWP 7342) exited]
[New Thread 0x7fffcd5e3700 (LWP 7343)]
[Thread 0x7fffcd5e3700 (LWP 7343) exited]

(simple-scan:7267): GLib-GObject-WARNING **: instance of invalid non-instantiatable type `(null)'

(simple-scan:7267): GLib-GObject-CRITICAL **: g_signal_emit_by_name: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed

Program received signal SIGSEGV, Segmentation fault.
0x0000000000416a4a in ?? ()
(gdb)