I'm attempting to attach a pdf document to a tax return for efiling.  The instructions I'm finding indicate to use the 'Link to Form' option indicating 'Form 8949 Exception Reporting Statement' which will attach the pdf to be efiled and not require a paper copy to be sent.  I am receiving an error that says 'The PDF file is linked to a nonexistent form.  Please verify the 'Link to Form ... field is correct.'  I'm not sure what is done improperly.