You are trying to push your application and specify a specific version of the runtime or language used by your application. The application fails to stage, giving an error like this.
2014-09-24T12:35:02.53-0600 [STG] ERR Expected dependency to exist but could not find it: <url>
When you see the error above, it means that the particular version you have specified is unknown to the build pack. This could be due to entering an incorrect version number or because the build pack needs to be updated to include support for the latest version of your runtime. Most build packs, like the Ruby, Go or Python build packs, need to be updated to support a new versions of their respective runtimes.
These updates may take a little time to become available in the default list of build packs on PWS. If you encounter this problem, you can often work around the issue by simply using a specific build pack instead of relying on the default included with PWS. You can do this by adding the -b argument to your cf push command or by adding the buildpack attribute into your manifest.yml file, and indicating the URL of the build pack you'd like to use.
Ex: command line
cf push -b https://github.com/my/buildpack
--- applications: - name: app-name memory: 128M instances: 1 path: . buildpack: https://github.com/my/buildpack
Here are links for the build packs supported on PWS.