stop user from select new tab in notebook

[calmar <mac calmar ws>]

Hi,
I have a notebook page where the user can select some things.
When the user wants to go to another page of the notebook, I wanted to 
verify the data he selected.
g_signal_connect (G_OBJECT (notebook), "switch_page",G_CALLBACK 
(refresh),NULL));

In this refresh function, I calculate if the textentries and so  have 
proper values...
If not, I tried to this: 
gtk_notebook_set_current_page(GTK_NOTEBOOK(notebook),3); ..in order he 
cant' move away from page 3.(in this callback function..from the 
'switch_page' ..callback.

This seems not to work unfortunately. ... maybe because when gtk sets 
the new page after my function maybe.
Does anybody know how I could do this?

(well another solution would be to take care of everything the user 
changes, and then react there directly..before he can try to leave the 
page).

I just thought I could also work when I just send him back to where he 
just were  .. which really doens't seem to work.

Thanks for any hints

marco candrian