When using OpenJPA within a container-managed environment and the configuration is using <jta-data-source> and/or <non-jta-data-source> elements with jndi names, the error messages produced when the lookup fails doesn't help with deciphering the problem:
<openjpa-1.1.0-SNAPSHOT-r422266:641891 fatal user error> org.apache.openjpa.persistence.ArgumentException: A JDBC Driver or DataSource class name must be specified in the ConnectionDriverName property.
Looking at the code, even if the jndi lookup causes an exception, the exception is eaten. This failure turns into a null datasource and then we fall into "normal" datasource processing with the openjpa.Connection* properties. That's when we produce the above message because there is no driver specified.
In this particular case, the user had a typo in his persistence.xml for the jndi name. It took too much debugging time to figure out that he had a typo.