gtk_text_inset -> 'text != NULL' error

[Yuushi <sakura texas net>]

The text widget is named 'txtInput' and it is already created and visible.
Also the text widget (txtInput) already contains text, I'm trying to use 
this
button (btnBold) to add more text and it gives me the following error.
(Note that I run my compiled program using the terminal to see signals 
and errors)
-------------------------------------------------------------------
Gtk-WARNING **: invalid cast from (NULL) pointer to `GtkText'
Gtk-CRITICAL **: file gtktext.c: line 953 (gtk_text_insert): assertion 
`text != NULL' failed.
-------------------------------------------------------------------

(Code Excerpt)

GtkWidget *txtInput;
void
on_btnBold_clicked (GtkButton *button, gpointer user_data)
{
   gtk_text_insert (GTK_TEXT (txtInput), NULL, NULL, NULL, ("<B></B>"), 
-1);
}


           Yuushi