Here is my 2 cents worth ........Reader/Acrobat uses a Windows API called MAPI to interact with Outlook. The message pops up (from Acrobat/Reader) informing the user that the program is attempting to communicate with the mail client. Once the Yes is chosen the actual call is made. Now there are 3rd party programs (Virus Scan programs) that will have policies embedded in them to stop the automation of this API call ....I think this is what is happening to you here. If you look at the virus scan software you can tell it that allowing Reader or Acrobat to automate Email is OK.
You can submit to a server-side script, which you have full control over the message and can customize the attachment the way you need such as file name or message body, and send a message response or redirect the user if the message has been sent or not. Using a server-side script bypasses Client Side Email software, so it can work for everyone who opens and submits the form, regardless of whether they have Outlook, Lotus, or a web based e-mail client.
Sounds like PDFEmail.net would work for your circumstance. PDFEmail.net runs scripts on Microsoft ASP.net web servers, and requires zero programming knowledge and virtually zero server setup. Just upload the scripts and libraries to your Microsoft .net web server virtual directory, and set the PDF submit button action URL to point to the script.
For more information, please visit: http://www.pdfemail.net/