Downloads\win32 problem

Hello,the problem i have at the moment is i have vista home basic i have usally been able to open downloads but now i am getting
c:\users\stan(thats me by the way)\Downloads\7z465 exe is not a valid win32 application. this is happening with every download not just 7 zip is their some setting i need to change ,i am new to vista so can any one help Thanks .