Error when trying to create a new bucket on Riak CS

error.txt

% s3cmd --debug mb s3://zbucket
DEBUG: ConfigParser: Reading file '/Users/jbbarth/.s3cfg'
DEBUG: ConfigParser: access_key->X2...17_chars...C
DEBUG: ConfigParser: bucket_location->US
DEBUG: ConfigParser: default_mime_type->binary/octet-stream
DEBUG: ConfigParser: delete_removed->False
DEBUG: ConfigParser: dry_run->False
DEBUG: ConfigParser: encoding->UTF-8
DEBUG: ConfigParser: encrypt->False
DEBUG: ConfigParser: follow_symlinks->False
DEBUG: ConfigParser: force->False
DEBUG: ConfigParser: get_continue->False
DEBUG: ConfigParser: gpg_command->None
DEBUG: ConfigParser: gpg_decrypt->%(gpg_command)s -d --verbose --no-use-agent --batch --yes --passphrase-fd %(passphrase_fd)s -o %(output_file)s %(input_file)s
DEBUG: ConfigParser: gpg_encrypt->%(gpg_command)s -c --verbose --no-use-agent --batch --yes --passphrase-fd %(passphrase_fd)s -o %(output_file)s %(input_file)s
DEBUG: ConfigParser: gpg_passphrase->...-3_chars...
DEBUG: ConfigParser: guess_mime_type->True
DEBUG: ConfigParser: human_readable_sizes->False
DEBUG: ConfigParser: list_md5->False
DEBUG: ConfigParser: log_target_prefix->
DEBUG: ConfigParser: preserve_attrs->True
DEBUG: ConfigParser: progress_meter->True
DEBUG: ConfigParser: proxy_host->localhost
DEBUG: ConfigParser: proxy_port->8080
DEBUG: ConfigParser: recursive->False
DEBUG: ConfigParser: recv_chunk->4096
DEBUG: ConfigParser: reduced_redundancy->False
DEBUG: ConfigParser: secret_key->lY...37_chars...=
DEBUG: ConfigParser: send_chunk->4096
DEBUG: ConfigParser: skip_existing->False
DEBUG: ConfigParser: socket_timeout->300
DEBUG: ConfigParser: urlencoding_mode->normal
DEBUG: ConfigParser: use_https->False
DEBUG: ConfigParser: verbosity->WARNING
DEBUG: Updating Config.Config cache_file -> 
DEBUG: Updating Config.Config encoding -> UTF-8
DEBUG: Updating Config.Config follow_symlinks -> False
DEBUG: Updating Config.Config verbosity -> 10
DEBUG: Unicodising 'mb' using UTF-8
DEBUG: Unicodising 's3://zbucket' using UTF-8
DEBUG: Command: mb
DEBUG: SignHeaders: 'PUT\n\n\n\nx-amz-date:Thu, 21 Mar 2013 06:15:36 +0000\n/zbucket/'
DEBUG: CreateRequest: resource[uri]=/
DEBUG: SignHeaders: 'PUT\n\n\n\nx-amz-date:Thu, 21 Mar 2013 06:15:36 +0000\n/zbucket/'
DEBUG: Processing request, please wait...
DEBUG: Establishing connection
DEBUG: get_hostname(zbucket): zbucket.s3.amazonaws.com
DEBUG: format_uri(): http://zbucket.s3.amazonaws.com/
DEBUG: Sending request method_string='PUT', uri='http://zbucket.s3.amazonaws.com/', headers={'content-length': '0', 'Authorization': 'AWS X2GOEX5TVL8FAYMQIIYC:H+4xthDGvLPZdquepY6VJtiIhFg=', 'x-amz-date': 'Thu, 21 Mar 2013 06:15:36 +0000'}, body=(0 bytes)
DEBUG: Response: {'status': 405, 'headers': {'date': 'Thu, 21 Mar 2013 06:15:35 GMT', 'content-length': '0', 'allow': 'GET', 'server': 'Riak CS'}, 'reason': 'Method Not Allowed', 'data': ''}
DEBUG: S3Error: 405 (Method Not Allowed)
DEBUG: HttpHeader: date: Thu, 21 Mar 2013 06:15:35 GMT
DEBUG: HttpHeader: content-length: 0
DEBUG: HttpHeader: allow: GET
DEBUG: HttpHeader: server: Riak CS
ERROR: S3 error: 405 (Method Not Allowed): 

I modify host.base and host.bucket and it working well, for example: when I install RiakCS on my machine with IP: 192.168.55.91 and port 9090, my host.base=192.168.55.91:9090 and host.bucket=192.168.55.91:9090/%(bucket)s

Hope it help!