Backups since Jan 1 have generated the following error on only one site.
S3 Service API: Validation errors: [ContentType] must be of type string
This is the only client site which backs up to their S3 account instead of mine, so I'm not sure if the issue is within AWS3 or BackWPup.
A search within the support forum shows this error occurring approximately 10 months ago with an earlier version. We are running 3.1.1 on WP 3.8.
Any clues for resolution?