Does emails having UNKNOWN_PARAMETER_VALUE contain a virus? Or is it a MIME problem?

I developed a program that sends emails (with attachments to clients). Now, some of the clients are asking what they should do with the emails with UNKNOWN_PARAMETER_VALUE.DAT? I'm quite sure that I've not sent attachments with those names. Only a few of the clients have received attachments with this. Is this a virus? If not, is this a MIME problem (FYI, some attachments have Chinese filename, I'm not sure if this might be a probable cause).

From stackoverflow

• It looks like a virus. At least it's listed here.