Salesforce bulk data load job fails with message 'InvalidBatch : Field name not found: Id'

After creating a bulk / batch job, I’ll sometimes see that it failed before even starting (failed batches:1, but with 0 records failed), with the following error:

InvalidBatch : Field name not found: Id

Annoyingly, this is caused by the inability of the Salesforce bulk import process to handle anything but ASCII.  Try saving your CSV again, making sure it’s in ASCII (called “CSV (Comma delimited)” in Excel) and not using UTF-8 or some other encoding.  No idea how you’re supposed to insert that new contact named José, though…