There is logic on bulk registrations to ensure that a contact uploaded is “contactable” in one form or another. The logic for sufficient data is as follows:

1. If the customer has a memberID, mobile phone or email 
then that is sufficient.
2. Lacking these they need at least one of 
firstname/lastname. Plus at least one of 
addressLine1/addressLine2. 
Plus at least one of a suburbTown/postcode/state.

When “insufficient data” is returned it means that the contact does not meet one or more of the required fields