If using the latest gtk2.tcz, make sure it's dependencies are updated too as the current gtk2 was built against the latest versions.
Do other gtk2 apps show a similar error message?
Specifically make sure that glib2 is updated.
A feature of the newer glib2 is:
------------
Overview of Changes from GLib 2.23.4 to GLib 2.23.5
===================================================
* New API addition: g_malloc_n() and friends used to implement an
overflow-safe family of g_new() macros.
-------------