GetTableCellValue "The control is not the type expected by the function".

I hope you can help me find why GetTableCellvalue is failing.
I'm getting "The control is not the type expected by the function".
  int calPanelId = LoadPanel(PARENT, "gui_main.uir", CAL_PANEL);
  Point p;
  p.x = 1;
  p.y = 1;
  double val = -1.0;
  int status = -1;
  status = GetTableCellVal(calPanelId, READY_TAB_TABLE, p, &val);
READY_TAB_TABLE is a table, according to the uir file:
gui_main.h:#define  READY_TAB_TABLE                  2       /* control type:
table, callback function: (none) */
I would appreciate any help you can give me.
Thanks,
Randy