Macro Virus?

We are experiencing an annoying problem with a so called macro virus in some excel files. I have checked the files out and they contain no macros, but when an individual sends the file in an email to someone else the file is quarintined by our Group Shield. I have scanned the file for viruses and have found nothing. On the alert we recieve it does not give a virus name just that a macro virus was found. I have checked out NAI's website on any info about macro viruses or the likes and could not determine much from them. We are not having any luck tracking down this thing. Any thoughts about Macro viruses or anything that might be usefull in this?

Thanks!

 

Could be a false positive. Why not submit the file(s) to NAI? General information regarding macro viruses can be found here.