I also use Amazon webservices. There is another way to do mass upload to your nirvanix account
Now i dont know how well you know the ec2 AMI structure. But you could load out your s3 content
within the /mnt/ directory of your AMI and use the nirvanix nput tool to upload your content to nirvanix.
The nput app uses curl so there might be some delay but your files are transfered completely.
And without any issues.
I have used the x.large AMI to upload lots of HD video to my nirvanix account.