One problem with OLE and Attachment fields is embedding files in db use up Access file size limit. I would only do that if a db is not expected to grow or to grow little. Instead, leave files in external folder and save path/filename in text field.
I don't know why External Data is not allowing link to table. I have no problem linking to table with attachment field and opening attachment via the table link.
Sometimes weirdness is due to corruption and some rebuilding may be needed.
If you want to provide files for analysis, follow instructions at bottom of my post.