Using Amazon S3 as storage option you can not use a bucket hosted in eu-central-1 (Frankfurt) due to newer autorize machnism:
The authorization mechanism you have provided is not supported. Please use AWS4-HMAC-SHA256.
Other server regions supporting older signature version but eu-central-1 requires signature version v4: http://docs.aws.amazon.com/de_de/AmazonS3/latest/dev/UsingAWSSDK.html
Any new region added after January 2014 only support AWS Signature v4:
http://docs.aws.amazon.com/de_de/AmazonS3/latest/API/sig-v4-authenticating-requests.html
I have not lokk up the source code for AWS function but i think you are using still version 3, so updating to version 4 is needed in order to work with buckets hosted in regions added after january 2014.