In Marketing Cloud's Automation Studio, we created an automated import file activity based on a file drop trigger (i.e. file naming pattern, not the folder-based drop). Even though the automation runs successfully, we're keep getting a validation error "field not found = 1, required fields = 1 " in the import file activity step (the second step is a SQL). We only have test data (i.e. one contact) in the source csv file that we want to test before going into production. General info: the delimiter is "comma", skip bad data and treat "" as text delimiters are turned on. I've checked the source csv file with notepad+++ and, ',' is indeed set as delimiter. We have no date fields in the source file and all data columns in the target DE are set as "Text" to avoid any mismatch on that account. We tried everything, but keep getting the above validation error.