Error Iam User not authorized You can register your master Amazon S3 account in CloudBerry Explorer and configure any IAM user that you want.
If you need those IAM users be able to use IAM manager as well, you should grant them required permissions (i.e. "iam:*").
If you would like those IAM users be able to access certain buckets only, so you can grant them full access for those buckets and no need for "iam" permissions then.