Make sure you have the ADPDF9.PPD printer description installed and Adobe PDF selected for the printer when you make the Postscript.
But better would be to export to PDF normally and use Acrobat's booklet printing.
Thanks for your answer!
I checked and couldnt find where should I install the ADPDF9.PPD.
I also tried to use Acrobat booklet printing but I wont print here, I need a PDF file ready to print to send someone else, and the Acrobat does not let me save the booklet.
What else can I do?
instructions for installing the PPD should be in the comments at InDesignSecrets » Blog Archive » Acrobat’s Adobe PDF Printer Replaced in Snow Leopard (I'm pretty sure the folder name is case sensitive).
Did this printer specifically request that you impose the booklet? That is normally his job and you just make things harder or impossible for him if you do it.