Please be more specific about the diagnostic and the context of your question.  First, under Main Form, there is no #12 although there is Sch E > 12 = Sch E.

It sounds like you may have linked the attachment to Sch E but did not index it to any activity.  Suggest you take another look at your entries on the e-file Attachment page.

If that's not the issue, you'd need to come back with more details.