you have to use an other container-configuration.
<configuration-name>Instance Per Transaction CMP 2.x EntityBean</configuration-name>
to your entity bean in jboss.xml. That solved our concurrency problems.
Thanks a lot for your answer :). Switching to the container-configuration solved our concurency problems, but another problem arised: it seems that the container is now not caching entities between transactions :( even we set commit-option to A. Do you have the same problem, or is it some other misconfiguration in our jboss?
you are right. That is the disadvantage of that configuration. Caching is not available between transactions for that container configuration.