Recently upgraded to Windows 7.  At first, upgraded to windows live mail 2012 also.  When I sent e-mail with attachment, the attachment would not open - said it was corrupt.  Then Windows live would keep sending multiple copies of the e-mail to the recipient.  So, uninstalled Windows Live Mail 2012, and reinstalled Windows Live Mail 2011.  Now, it only sends two e-mail to the recipient.  The first attachment is corrupt and won't open.  In the second e-mail, the attachment will open.