Windows 7 Ie 8 Error “won’t allow user to download only pdf files to view”

Dell Vostro Desktop Computer, Windows 7 Home, IE 8, Avast Anti-Virus. Adobe Reader current version, all updates run, Office Professional 2007. Customer uses Windows Live Mail. When customer attempts to view a PDF file, the following error is generated: “your current security settings do not allow this file to be downloaded”. I have run all updates, downgraded IE from 9 to 8, disabled Avast, to no avail. The Microsoft answer is to to Internet Options, Security, Custom, Settings, Downloads – File download options, enable download files, to no avail. I have always made the changes, closed IE then reopened IE, all to no avail. Please help me.