Amazon S3 backup fails without any specific errors.

Hi,

Operating system : Ubuntu Linux 14.04.5
Virtualmin version : 5.04.gpl
Webmin version : 1.821

I noticed that the Amazon S3 backup fails for one of my specific virtual domains , but there are no specific errors in the backup log, there is just a mention that the backup for that domain failed (backup is marked as partially successful)

Is there any log file i could check for additional details?

Local file backup is successful for that same virtual domain.
One thing I noticed is, for the same virtual domain that the backup fails to upload to S3, there is only 1 local backup file. i.e. server1.tar.gz
And for the other virtual domain that works, there are 3 local backup files, i.e. server2.tar.gz, server2.tar.gz.info, server2.tar.gz.dom

Later I installed s3cmd and used s3cmd put to upload the file with the same set of key and secret, that worked.