uscore_to_wincaps doesn't check the input parameters uscore, it appears to be 
NULL in some cases:
#0  uscore_to_wincaps (uscore=0x0) at dbus-gobject.c:64
#1  0x00140ce2 in gerror_to_dbus_error_message 
(object_info=Variable "object_info" is not available.
) at dbus-gobject.c:842
#2  0x00141cf3 in gobject_message_function (connection=0x8b51d78, 
message=0x8b53498, user_data=0x8b50240) at dbus-gobject.c:1219
#3  0x05766af9 in _dbus_object_tree_dispatch_and_unlock (tree=0x8b51bd8, 
message=0x8b53498) at dbus-object-tree.c:842
#4  0x0575132c in dbus_connection_dispatch (connection=0x8b51d78) at 
dbus-connection.c:3820
#5  0x0013d26d in message_queue_dispatch (source=0x8b52210, callback=0, 
user_data=0x0) at dbus-gmain.c:113
#6  0x00514ffd in IA__g_main_context_dispatch (context=0x8b515d8) at 
gmain.c:1916
#7  0x0051828f in g_main_context_iterate (context=0x8b515d8, block=1, 
dispatch=1, self=0x8b50550) at gmain.c:2547
#8  0x00518639 in IA__g_main_loop_run (loop=0x8b50988) at gmain.c:2751
#9  0x08051be3 in sniffer_dbus_main () at dbus/wireshark-dbus-sniffer.c:229
#10 0x0804fcc0 in main (argc=Cannot access memory at address 0x50


Here is the function declaration that has trigger the crash:
    <method name="getInstance">
      <annotation name="org.freedesktop.DBus.GLib.CSymbol" 
value="sniffer_get"/>
      <arg type="s" name="name" direction="out">
        <annotation name="org.freedesktop.DBus.GLib.ReturnVal" value="error"/>
      </arg>
    </method>