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...