Adobe Acrobat 9.0 - forms can not be submitted

Adobe Acrobat 9.0 - I created an online form with a submit button.  I posted the form on our website and we have found that when someone fills in the form and presses SUBMIT they get an Adobe Reader message that says "this form has a submit button on the bottom, you can fill out the fields but cannot submit."  How do I make this a submittable form? BTW-they are able to save the form and fax it to us.  Thanks for any help you can give me!!!