Note: Are you still running Weblogic 8.1 - it's already reached end of life. Also ejbgen works with EJB 2.x and over the last 2 years, development has moved on to EJB 3, so i'd advise you to catch up on those.
Now to your specific problem.
Your code does not seem to have the required annotations for ejbgen to work.
Annotations like this which are used in generation of the descriptors.
* @ejbgen:entity
* ejb-name = containerManaged
* table-name = ejbAccounts
* data-source-name = examples-dataSource-demoPool
* prim-key-class = AccountPK
* invalidation-target = ServiceDesignEJB
As your URL says the code in the tutorial has the right data as a sample - make sure you replicate those correctly in your own code.
EJBGen uses annotations in the bean file to generate the deployment descriptor files and the EJB Java source files. EJB files in the MedRec application are already annotated for EJBGen.
For another version of ejbgen, see http://www.beust.com/ejbgen/