S3cmd error on sync: S3 error: 400 (InvalidRequest)

Currently, what you're trying to do can't be done in a single operation. Move in S3cmd to the API is essentially a copy and delete all in one and it's a restriction of the copy operation.

http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectCOPY.html

You can store individual objects of up to 5 TB in Amazon S3. You create a copy of your object up to 5 GB in size in a single atomic operation using this API. However, for copying an object greater than 5 GB, you must use the multipart upload Upload Part - Copy API

http://docs.aws.amazon.com/AmazonS3/latest/dev/CopyingObjctsMPUapi.html

The examples in this section show you how to copy objects greater than 5 GB using the multipart upload API. You can copy objects less than 5 GB in a single operation.

Take care with your trailing slash (or lack of slash) in path names. It makes a difference.

http://s3tools.org/s3cmd-sync

Important — in both cases just the last part of the path name is taken into account. In the case of dir1 without trailing slash (which would be the same as, say, ~/demo/dir1 in our case) the last part of the path is dir1 and that’s what’s used on the remote side, appended after s3://s3…/path/ to make s3://s3…/path/dir1/….

On the other hand in the case of dir1/ (note the trailing slash), which would be the same as ~/demo/dir1/ (trailing slash again) is actually similar to saying dir1/* – ie expand to the list of the files in dir1. In that case the last part(s) of the path name are the filenames (file1-1.txt and file1-2.txt) without the dir1/ directory name. So the final S3 paths are s3://s3…/path/file1-1.txt and s3://s3…/path/file1-2.txt respectively, both without the dir1/ member in them. I hope it’s clear enough, if not ask in the mailing list or send me a better wording ;-)