Just so everyone will know --- the answer to this question from Lacerte was:  "Most of the efile errors that we get from c-corps are related to Form 1120-H, so our generic message mentions 1120-H.  That has nothing to do with the problem in your case. Many times the file name for the attachment has a space in it, or the file name is too long, and the IRS rejects it.  When you see the code 0(00) and the Field: /Return/ReturnData/BinaryAttachment, it usually means that there is a problem with the attachment."  In my case,  I just removed the attachments and the 1120's e-filed successfully.  It would have been really nice if the first 2 people at Lacerte that we called yesterday had been able to share this answer.  Nope, had to wait for someone a little higher up to help us!  😞