Prohibited Files Download

For the last two and half years I have been using Windows Live Mail and have been able to send and receive file attachments such as Excel; Word; pdf and jpg without any problems. Now, and within the last three days, all of my outgoing and incoming attachments have been declared as Prohibited Files Download which cannot be opened. The Windows Live Mail suggested solution to this problem is to un-click the security option relating to attachments which then has a footnote that states that this option should not be used as will open the computer to viruses, etc. Some help that is! Any suggestions please.