It looks like you have been trying to mix a number of principles discussed on the web into one and unfortunately this is not how it works.
The 'java:comp/env' namespace is a namespace that each compnent has its own private version of. In the deployment descriptors of a component using ejb-ref and resource-ref (and different variations of these) you can specify what needs to be references from the components namespace. These can really be thought of a symbolic links that can be altered so the component does not need to be recompiled if the resources it used are changed.
There is another namespace the 'java:' namespace, this contains items that are global to the container but can only be accessed within the container. This (as you have already worked out) is the default place the resource adapter will be bound.
In your deployment descriptor you have configured it to bind to the 'java:' namespace using the same String that would be used to access the components namespace.
Try removing the 'comp/env' from the name your resource adapter is bound to and adjust the client accordingly and see if that works.