Read the warning message VERY carefully -- does it say that the file has a virus? Or does it say something general like

" Some files may harm your computer and may contain viruses. Do not download files from people you not know or trust"

I get that general warning with ANY attachment at work -- and it is a GENERAL warning not one SPECIFIC to that particular file. Just a general warning to take care and be aware.

If you have a SPECIFIC warning -- be sure to respect it.