Above info is very conceptual, thanks for sharing. I had exact same error but in Adobe standard Campaign. Its interesting how standard handles this scenario. It creates blank personalized fields in test email sends and we do not have to add any alias or sample data. But when I got same error for actual profile, I found that there were duplicate additional data for same profile and I was using aggregate instead of collection for "Type". Example: One profile registered same webinar twice and using...

Thank you for confirming.