GTK_IS_SPIN_BUTTON problems

[Aaron Pendergrass <aaron nearest-exit org>]

Hi all,
I'm having a problem with my app when I call GTK_IS_SPIN_BUTTON(); from a callback function...
the relevant code is to the effect of 

typedef struct{
  GtkWidget *widget;
  char **string;
  int *integer;
  gboolean *boolean;
} configOption;

/*...various code.....*/
gint set_configurations(GtkWidget *widget, configOption *options)
{
  int i;
  for(i=0;i<4;i++)
    {
      if(options[i].widget != NULL){
        if(options[i].integer != NULL)
          {
            if(GTK_IS_SPIN_BUTTON(options[i].widget))
              {
                *options[i].integer=gtk_spin_button_get_value_as_int(GTK_SPIN_BUTTON(options[i].widget));
              }
          }
..../*other checks to see if it is a different type of widget/variable*/


but the app is conking out at the call to GTK_IS_SPIN_BUTTON.
Am I calling the wrong function or something. I couldn't find an explanation of the GTK_IS_* functions 
online.  (gtk 1.2)
thanks in advance
aaron