Bug#510326: How to diagnose what went wrong?

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I don't know if this is of any help but I used 
ulimit -c unlimited

and launched brasero from gnome-terminal
And I got this when I failed to erase a dvd-rw (brasero closed)

(brasero:3802): GLib-GObject-CRITICAL **: g_type_instance_get_private:
assertion `instance != NULL && instance->g_class != NULL' failed

I'm not sure if I have the same problem. In which log should I check for
errors? Thank you in advance.