What versions of reader allow filling of form created in Acrobat 9?

I apologize if this is a repeat question.

I have created a form with many fields and checkboxes. I have enabled the save ability and emailed as an attachment to many of my clients. Some can edit, save and attach to an email to send back to me without problems. Others fill it out and save, but the content is empty. I suspect their version of Reader is not up to date. So.....

What versions of Reader will work correctly with a form created with Acrobat Standard 9.3 ?

Is there anyway of having Reader warn someone that their currently installed version will not work ?

It seems that older versions of Reader lead users to believe that they are filling out a form correctly when in fact they are wasting their time because the information is not saved.

Thanks for any thoughts.