I would like to list the attachments in a single field, to be referenced using a relationship in another form?

You do not need to concatenate the actual file attachments, you need to concatenate a link to each file attachment.

Here is the syntax to make a link to display a file attachment.  Get it working on the parent table and then use it in any List (...) formuals or lookups


URLRoot() & "up/" & dbid() & "/a/r" & [Record ID#] & "/e30/v0"


Replace the 30 with the fid of the field holding the file attachment and you are all set.