DWA Attachment not looking like an attachment and giving an Unknown Command Exception error

I have users who when they get an email with an attachment, it doesn’t look like a normal attachment. It looks like this:

When they click on the link, a new window opens with the Unknown Command Exception error.

Can anyone tell me why this is happening? The only thing that I have done is to edit the form7.NSF for the new DST change.

Thanks