If you are receiving the following error on your Migrate Page, then please check the file names.
If your File contains any NON-PRINTABLE UNICODE characters, then please change those file names to avoid this error.
You can find the file that contains the bad characters by adding a LIMIT clause in your SOQL filter.
PS: View Drag, Drop & Upload Files to Amazon S3, a Salesforce AppExchange app for moving files from Salesforce to Amazon S3: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3000000B5ZPqEAN