I am getting the same error.  Mine is on a partnership return.  I am not filing form 3800 but I do have several attachments.  Not more than I have had in previous years.  My error is showing up on the information worksheet and it does not say what form is causing the error.  Btw, the review process gets hung up in the middle of the diagnostics.  Not sure if that is happening for the same reason or not.    Going to remove my attachments and see if that clears it up.