That bug has been described on https://launchpad.net/distros/ubuntu/+source/gnome-system-tools/+bug/26117

"After fiddling with System > Administration > Shared folders, it just doesn't
work. Now, when I try to open it, it loads (cursor shows as "work in progress")
for many seconds, then all buttons are blanked, and the list is empty, hence I
can't do anything.
...
*** glibc detected *** double free or corruption (fasttop): 0x08289638 ***
...
> Could you get a valgrind log? Install the "valgrind" package and use "sudo valgrind shares-admin", it should make the application really slow to start but point some issues you may have, especially was is creating the "*** glibc detected *** double free or corruption (fasttop): 0x08289638 ***" you copied to your first comment
...
==9561== Invalid free() / delete / delete[]
==9561== at 0x1B8FF44F: free (vg_replace_malloc.c:235)
==9561== by 0x1C166053: g_free (in /usr/lib/libglib-2.0.so.0.800.3)
==9561== by 0x8050A88: gst_share_nfs_new_from_xml (in /usr/bin/shares-admin)
==9561== by 0x8051286: table_add_share_from_node (in /usr/bin/shares-admin)
==9561== by 0x80517A2: transfer_xml_to_gui (in /usr/bin/shares-admin)
==9561== by 0x1C08FAB2: g_cclosure_marshal_VOID__VOID (in /usr/lib/libgobject-2.0.so.0.800.3)
...
Itś been a while, but i found a good workaround. Use Synaptic to remove the package "nfs-kernel-server". Be sure you do a Complete removal including the config files.
After that, reinstall the same package and you're done. It worked in my case anyway.
As this worked, I suspect there is something wrong in a configuration file.
..."