Comment 36 for bug 666211

As a matter of practicality, given this and other problematic bugs w/ EC2 on the stock Maverick and Lucid kernels (there are several that range from annoying to flat-out unreliable or un-(re)-bootable), I had been running my Maverick-based instances with the Karmic kernels pretty successfully for a long time (by adding Karmic repos to sources.list and installing linux-image-2.6.31-307-ec2 from them and deleting the Maverick kernel as part of my cloud-init script on first boot).

I'd recommend that to you now (and you still can if you must, using the old-releases.ubuntu.com mirror), but Karmic has now been dropped from support some months back. This leaves basically no stable, supported option for an Ubuntu-based distribution with a reasonably-decent quality kernel for EC2. I'd recommend switching distros; these problems have been simmering far too long to expect a sudden fix to come your way.