(gdb) bt
#0  0x0062d402 in ?? ()
#1  0x0071fcce in __lll_mutex_lock_wait () from /lib/libc.so.6
#2  0x006b24e8 in _L_lock_43 () from /lib/libc.so.6
#3  0x006ac35d in ptmalloc_lock_all () from /lib/libc.so.6
#4  0x006d59e0 in fork () from /lib/libc.so.6
#5  0x008ecad0 in fork () from /lib/libpthread.so.0
#6  0x080b9250 in crash_handler (sig=6) at crash.c:523
#7  <signal handler called>
#8  0x0062d402 in ?? ()
#9  0x00672ee9 in raise () from /lib/libc.so.6
#10 0x006744f1 in abort () from /lib/libc.so.6
#11 0x006a753b in __libc_message () from /lib/libc.so.6
#12 0x006aea68 in _int_free () from /lib/libc.so.6
#13 0x006b1f6f in free () from /lib/libc.so.6
#14 0x00b6b5a1 in g_free () from /usr/lib/libglib-2.0.so.0
#15 0x00ea5ba1 in vcal_item_set_xml (folder=0xbdf50e0, item=0xbdf53a8, tag=0xa6d42b8) at vcal_folder.c:221
#16 0x080d90b3 in xml_to_folder_item (nodedata=0xa6d42a8, data=0xbdf50e0) at folder.c:3506
#17 0x081c08dc in g_node_map (node=0xa6c3c00, func=0x80d9040 <xml_to_folder_item>, data=0xbdf50e0)
    at utils.c:3901
#18 0x080d97e4 in folder_get_from_xml (node=0xa6c3bb0) at folder.c:3571
#19 0x080d9ab4 in folder_register_class (klass=0xef58c0) at folder.c:137
#20 0x00e9702d in vcalendar_init () at vcalendar.c:1531
#21 0x00e96ee0 in plugin_init (error=0xbfc5cd98) at plugin.c:44
#22 0x081ccb20 in plugin_load (
    filename=0xbfc5ad98 "/opt/claws-mail-work/lib/claws-mail/plugins/vcalendar.so", error=0xbfc5cd98)
    at plugin.c:358
#23 0x081cce5f in plugin_load_all (type=0x820dd70 "GTK2") at plugin.c:425
#24 0x0810615b in main (argc=Cannot access memory at address 0x0
) at main.c:994
(gdb) kill