Afair, this was a known issue which was fixed in the later versions.

(CapeDwarf version on OpenShift is pretty old ...)

luksa can tell you more.

Perhaps this could be a workaround:

If you can work with dev type of login,

you can remove the system property "com.google.appengine.runtime.environment" we somewhere set in OpenShift + CD script.

(this property needs to be set to "Development")

* http://capedwarf.org/documentation/user-guide/

Can you post the stacktrace or any other info?