So, clearly, no-one knows what this error code means and the fact that Profile has not seen fit to give any diagnostics as to what the problem might be is annoying.  Saying the return 'might' have incorrect information is hardly helpful.  Instead of awarding badges, cheers, congratulations for reading xxx articles, maybe some help on a subject?

Hope this helps people.  Apparently the T3 is now similar to the T1 and if you have a rental schedule but don't show the address for the estate on that rental schedule, it will fail in the efiling process for the T3 return itself.  The T3 slips with summary filed fine, but the T3 return failed.  Hopefully Profile will get it together and show us the error message as they do in the T1 portion of the software when we do not have the address in the T776 or T2125, etc...

Thanks for your reply.  No rental or business schedules.  Just investments.  Have been through this return several times, see nothing wrong.  Paper filed.  Old school still works, until our friendly folk at CRA decide that puts too much of their work back on them.