I'd been running version 1.0.1 for a while and decided to update to 1.6.0 and found uploads no longer work. Here is what I see comparing 1.0.1 with 1.6.0 with the same file, same settings:
Version 1.0.1:
[1 of 1]
13898578 of 13898578 100% in 3s 3.56 MB/s done
Version 1.6.0:
[1 of 1]
5373952 of 13898579 38% in 1s 2.77 MB/s failed
WARNING: Upload failed:([Errno 104] Connection reset by peer)
WARNING: Retrying on lower speed (throttle=0.00)
WARNING: Waiting 3 sec...
[1 of 1]
6684672 of 13898579 48% in 1s 3.50 MB/s failed
WARNING: Upload failed: ([Errno 104] Connection reset by peer)
WARNING: Retrying on lower speed (throttle=0.01)
WARNING: Waiting 6 sec...
[1 of 1]
5439488 of 13898579 39% in 1s 2.64 MB/s failed
WARNING: Upload failed: ([Errno 104] Connection reset by peer)
WARNING: Retrying on lower speed (throttle=0.05)
WARNING: Waiting 9 sec...
[1 of 1]
1638400 of 13898579 11% in 2s 736.68 kB/s failed
WARNING: Upload failed: ([Errno 32] Broken pipe)
WARNING: Retrying on lower speed (throttle=0.25)
WARNING: Waiting 12 sec...
[1 of 1]
589824 of 13898579 4% in 2s 216.75 kB/s failed
WARNING: Upload failed: ([Errno 104] Connection reset by peer)
WARNING: Retrying on lower speed (throttle=1.25)
WARNING: Waiting 15 sec...
[1 of 1]
327680 of 13898579 2% in 6s 50.97 kB/s failed
ERROR: Upload of '' failed too many times (Last reason: Upload failed for: '')
Someone else had reported the same issue on the forums a few months back...
http://sourceforge.net/p/s3tools/discussion/618865/thread/62ff8a6d/