This will only occur if you are trying to import to adverity Insights. As explained here, Insights only supports one column with type Date (day) and does not currently support DateTime column types. If you want to import additional date columns e.g. campaign start date, use column type String.
STEP 1: IDENTIFY WHICH COLUMNS ARE CAUSING THE ISSUE
Click on the extract that caused the import error and in the metadata section, under datastream_extract_mapping, you see all mapped columns, and their column types. Identify which date columns are specified as 'type': 'date'. Only one column, day, should be configured in this way. All other date columns should be type String.
Hint: Use CTRL + F and paste 'type': 'date' to see which fields are mapped to a date type column
STEP 2: CHANGE THE TYPE OF THE COLUMN
After finding out which additional date columns were incorrectly configured, change them to type string. Under Schema, search for the column(s) and change their type.
STEP 3: REQUEUE THE EXTRACT
After you have made sure that only one column has type Date, and all others are type String, you can requeue the extract.