Comment 6 for bug 1388860

This sounds like a case of someone using default-vpc and it has a default subnet on most availability zones (a-d) but does *not* have a default subnet on us-east-1e.
Switching to eu-west-1 means you are using a different set of configured networks (either not in VPC or with a different set of subnets configured).

We are looking at configuring VPC on Amazon in this cycle, but I don't believe that bigger solution is reasonable for 1.21.

Its possible we could just skip zones that don't have a subnet configured?

This sort of failure sounds very specific to a given user's account and how their EC2 environment is configured, as such it will be hard for us to reproduce and fix. If it fails reasonably reliably for you, we can try to determine some workarounds and work with you to see if it fixes things.