If a version number contains a + (as it does in CDH) then the URL created for the script location http://whirr.s3.amazonaws.com/VERSION is wrong. It should escape the VERSION string.
Here's a fix. I tried leaving the definition of run-url-base in the properties file, but nested properties don't work so I moved that logic into ClusterSpec. (I tried using http://commons.apache.org/configuration/userguide/howto_basicfeatures.html#Customizing_interpolation to create a urlencode lookup but you can't have nested variables, and maven also won't replace $
if it is embedded in another variable).
This should be ready for commit. I've tested it manually too.
I've just committed this.