I'm importing some data into a data extension via Data Extensions, and most of the data has gone in without problems. However, it's highlighted about 100 rows as being unable to import due to 'CaseSensitiveSalesforceID'.
We aren't using Salesforce IDs in Marketing Cloud - we don't have the connector to Sales Cloud, and this data has not come from Salesforce. It's not even clear which field this refers to. What is causing this?