I tried to start one of my Amazon EC2 AMI’s a few day’s ago, and received the error:

Insufficient capacity

Which I found was very weird. I think that’s just we’re cloud computing stands out from traditional computing, the possibility to add capacity on demand. I found out that I had to AMI’s with the same source (the manifest).

I de-registered one of them, but still received the same error.
Today I tried again (yes, I am stubborn) by starting the one AMI that was left. This resulted in a completely different error:

registered machine image manifest for ami-******* and manifest in S3 differ. Has the image been rebundled but not re-registered.

I solved it by firing up the EC2 API Command Line Tools, and executing the command:

ec2-register <bucket>/<name.manifest.xml> -n <Name>

For the parameter Name I opened up CloudBerry Explorer for Amazon S3 and opened the manifest.xml file that was causing the problem. Inside this file there is a xml tag named <name>, Use this one to register your AMI.