Readers can't comment on my PDFs

I was recently upgraded from Acrobat 8.1 Standard to Acrobat 11.0 Stamdard. Most people here have Acrobat Reader 9.

I want to be able to send out PDFs for review and have them comment in the PDF. My security settings allow commenting. Howeve, when someone open the PDF in Reader 9, comment is disabled.

What am I missing?

Thanks

Keith