Email

Suddenly I am unable to open and preview pdf documents I've attached to email before sending. I am able to open these documents before I attach them, I am able to go to the sent mail box and open them after I have sent the email. I am using Adobe Reader 9.1, running Windows Vista, using Outlook 2007 for email. I tried switching to Windows mail but had the same problem. I was able to open & preview these documents up to about a month ago, then things changed. Does anybody know if there has been an update recently that might have caused this? Any idea how to fix?