Scotty, the attachment is being saved in the secretary’s temp directory on her computer. That’s what the “invalid or nonexistent document” is. We’ve seen the same problem with users who specify a local signature file, rather than using a plain text signature (which is stored with the mailfile). The attachment may actually *be* there, but the specified path is invalid because it refers to the secretary’s temp file rather than the mailfile owner’s.
Can the other user (mailfile owner?) actually open the attachment? If so, accessing it and resaving it might resolve the issue. Another way to do it is to make sure that the attachment path is the same for both users and equally accessible — a shared drive, for instance.