exactly the same problem having HD5770, w7 x64
the error comes from AMD server files BECAUSE
the size file in this link says "184 mb", when the browser ask for save the file, say 184mb too, but the result is not.
http://support.amd.com/us/gpudownload/windows/Pages/radeonaiw_vista64.aspx
but at last, is the same trash autodownloaded with catalyst manager (74MB)