For the future for us to help you better, can you give the diagnostic # and the whole text of the diagnostic? The easiest way I've found to get the whole text selectable to copy-paste is to PDF the diagnostics report (or a preparer file copy). Then we'd be better able to weigh in on whether that diagnostic could be suppressed in efile.

If I understand your request correctly, is this activity 1) profitable and 2) subject to SE tax?  Is your client in a community property state?

If there aren't SE tax considerations, can you just choose to assign it to either the husband or the wife?  I'd ask the client if they have a preference.

If there are SE tax considerations, I'd probably just reenter a second SchF, apportion 50% and give one to the husband and one to the wife.