javascript problems

We have design ad application that use pdf form.
But in certain situation with different readers (versions 8.0, 7.0, 5.0, not 6.0)
some script have problems to find the object in the document,
when this object (button/filed/combo...) is outside the visible window,
for example the second page.
 
the script run at the open window event, and is soo simple:
 
var obj=app.getValues("nameobj");
 
this return null in certain situations.
 
why this happen?
 
do you have any idea?
 
some person have told me that my pdf is malformed.
i have the "field widgets" but not the "entries in the Fields dictionary".
but i have use Acrobat Professional 6.0.5 for design.
You think that the function "Reduce size..." present in the Professional can generate this problem?
  
thank you
Aristide Di Lauro