Getting SignatureDoesNotMatch when attempting to download a file in S3

So, I'm writing a tool that will be uploading CSV files to Linode S3. It is a Java process, using the AWS SDK to interact with Linode S3.

It is successfully persisting files up, however if I attempt to download them using the Linode Object Storage UI, I get the following:

<error> SignatureDoesNotMatch <requestid>tx00000000000000531d6e3-0061bf808f-27fa824-default</requestid> <hostid>27fa824-default-default</hostid> </error>

So I'm a bit confused as to why this is happening. There are no errors on uploading the file. I've tried computing the MD5 and adding it to the metadata on upload myself, and not (presumably letting the S3 client do it) - it makes not difference, the file is not downloadable.

The file content length is correct - so it would appear to be there - but I'm at a loss as to how to download it or indeed view it.

Any clues out there?