Thanks Kirk. PM_log.zip attached.
I can see some more interesting error in it leading up to the one I was seeing in the Upload log:
[Fri May-04-2018 21:36:27.786][b154f000][1426668] [0fe6b1bc] Exception while checking for bucket The bucket you are attempting to access must be addressed using the specified endpoint. Please send all future requests to this endpoint., <?xml version="1.0" encoding="UTF-8"?>
<Error><Code>PermanentRedirect</Code><Message>The bucket you are attempting to access must be addressed using the specified endpoint. Please send all future requests to this endpoint.</Message><Bucket>images.staggarts.com</Bucket><Endpoint>images.staggarts.com.s3.amazonaws.com</Endpoint><RequestId>D54387D1481653D9</RequestId><HostId>Qz2fX3bZJ0mei2a44FkEI/oB0zE91R5I5yGUTBALXJv6k68mABsNLPWtxnIDB5wl1EoG5zp6za0=</HostId></Error>
[Fri May-04-2018 21:36:28.775][b154f000][1426692] [0fe8222c] ruby-bridge: exception: #<AWS::S3::BucketAlreadyOwnedByYou: ./ruby/lib/ruby/1.8/aws/s3/error.rb:38:in `raise': Your previous request to create the named bucket succeeded and you already own it.>
I've done some more research and a little experiment. It appears that this is the age old problem of bucket region. Several pages on the web indicate that the error(s) above a generated because "bucket region is incorrect" and I've read a few posts on this forum that suggest that PM only works with the default "US Standard" region.
As an experiment I created a bucket in the US East region with identical configurations etc to my first bucket (Asia Pacific [Sydney] - because I live in Australia). I have no problem Uploading to this bucket. "So problem solved" I here you say. Sorry but no this just means that PM's S3 bucket support has been programmed from a parochial point of view.
Looking over S3 AWS documentation etc there appears to be a misnomer that S3 bucket region makes no difference. This seems to be partially because in the S3 dashboard the phrase "S3 does not require region selection" appears under the region selection list. However when you create a bucket you get to choose a region, why?
Apparently quoted from S3 docs.
"Amazon S3 creates bucket in a region you specify. You can choose any AWS region that is geographically close to you to optimize latency, minimize costs, or address regulatory requirements. For example, if you reside in Europe, you might find it advantageous to create buckets in the EU (Ireland) or EU (Frankfurt) regions. For a list of AWS Amazon S3 regions, go to Regions and Endpoints in the AWS General Reference."
I may have misinterpreted the various docs. I've read on this so I'm happy to be proved wrong but this all suggests to me that the PM S3 Uploader really needs a way of choosing the bucket region.