invalid utf-8 string pango warning

[Rudra Banerjee <rudra banerjee aol co uk>]

Hello gurus,
I am a novice(both in C and in gtk+), but managed to create a parser
that will create a tree from the parser.
The problem is, in the minimal example posted in fpaste, if the line
264-266 is uncommented, i.e. I parse the same file twice, I get 
"Pango-WARNING **: Invalid UTF-8 string passed to
pango_layout_set_text()"

This reading the same file twice matches the exact behavior when I open
and parse the file using 

  "filename=gtk_file_chooser_get_filename(GTK_FILE_CHOOSER(dialog));
    g_file_set_contents(filename, buffer, -1, &Err);"

The code, sample example and makefile is at:
http://paste.fedoraproject.org/13915/04195136/
http://paste.fedoraproject.org/13917/04584136/
http://paste.fedoraproject.org/13918/13693046/

Any help on where I am going wrong will be appreciated.