Hi Shahriar,
Thanks for your reply.
The bucket with the error I created directly in the Amazon online dashboard. I can not open it via my WordPress websites dashboard using the Download Manager Amazon S3 plugin.
Now I created a new bucket via my WordPress website with the Download Manager Amazon S3 plugin. This bucket works alright! Buckets created via the WordPress websites dashboard seem to work fine but the buckets I create via the Amazon dashboard give an error if I want to open them via the Download Managers Amazon S3 plugin.
Now I know this, my problem is solved!
With kind regards,
Juliet