[GtkGLExt] Compile error "virtual thunk"

[jlm <jsado_sc4 earthlink net>]

I am upgrading from gtkglextmm 1.1.0 to 1.2.0. I believe I have made all 
of the necessary changes to my code, but when I link I get this error:

/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.6/../../../libgtkbonus.so: 
undefined reference to `virtual thunk [v:0,-24] to 
Gtk::GL::DrawingArea::~DrawingArea [in-charge]()'
/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.6/../../../libgtkbonus.so: 
undefined reference to `virtual thunk [v:0,-24] to 
Gtk::GL::DrawingArea::~DrawingArea [in-charge deleting]()'

Now I have a library (libgtkbonus) that uses gtkglextmm, as well as the 
main program. In the library I use the Gtk::GL::DrawingArea, but not in 
the main program. I have compaired my use of this widget to that in 
simple-darea.cc, and can find only one difference. The 
Gtk::GL::DrawingArea in simple-darea.cc is initialized with a "config" 
parameter, and mine is not. I have my glconfig code inside the 
sub-class' constructor.

But I don't think this is what the problem is. At any rate my library 
compiles just fine. It is when linking it in with the program that I get 
the above error.

Does anyone know what this is?

Thanks