I am trying to use 2 persistence units within the same transaction in a JEE application deployed on Glassfish.

The 2 persistence units are defined in persistence.xml, as follows:

<persistence-unit name="BeachWater">
<jta-data-source>jdbc/BeachWater</jta-data-source>
...
<persistence-unit name="LIMS">
<jta-data-source>jdbc/BeachWaterLIMS</jta-data-source>
...

These persistence units correspond to JDBC resources and connection pools which I had defined in Glassfish as follows (include one here as both are identical apart from names & database connection info):

JDBC Resource:
JNDI Name: jdbc/BeachWaterLIMS
Pool Name: BEACHWATER_LIMS

Connection Pool:
Name: BEACHWATER_LIMS
Datasource Classname: com.microsoft.sqlserver.jdbc.SQLServerConnectionPoolDataSource
Resource Type: javax.sql.ConnectionPoolDataSource

There are 3 stateless session beans, LimsServiceBean, AnalysisServiceBean and AnalysisDataTransformationServiceBean.

Here are the relevant snippets from LimsServiceBean:

@PersistenceContext(unitName = "LIMS")
EntityManager em;
...
public ArrayList<Sample> getLatestLIMSData() {
    Query q = em.createNamedQuery("Sample.findBySubTypeStatus");
    return new ArrayList<Sample>(q.getResultList());
}

From AnalysisServiceBean:

@PersistenceContext(unitName = "BeachWater")
EntityManager em;
...
public ArrayList<AnalysisType> getAllAnalysisTypes() {
    Query q = em.createNamedQuery("AnalysisType.findAll");
    return new ArrayList<AnalysisType>(q.getResultList());
}

And from AnalysisDataTransformationServiceBean:

@EJB
private AnalysisService analysisService;

@EJB
private LimsService limsService;

public void transformData() {
    List<AnalysisType> analysisTypes = analysisService.getAllAnalysisTypes();
    ArrayList<Sample> samples = limsService.getLatestLIMSData();

This call to limsService.getLatestLIMSData() caused the following exception:

     [exec] Caused by: javax.ejb.TransactionRolledbackLocalException: Exception thrown from bean; nested exception is: Exception [TOPLINK-4002] (Oracle TopLink Essentials - 2.1 (Build b60e-fcs (12/23/2008))): oracle.toplink.essentials.exceptions.DatabaseException
 [exec] Internal Exception: java.sql.SQLException: Error in allocating a connection. Cause: java.lang.IllegalStateException: Local transaction already has 1 non-XA Resource: cannot add more resources.

Having consulted this page, http://msdn.microsoft.com/en-us/library/ms378484.aspx (among many others), I tried changing the definition of the connection pools to:

Connection Pool:
Name: BEACHWATER_LIMS
Datasource Classname: com.microsoft.sqlserver.jdbc.SQLServerXADataSource
Resource Type: javax.sql.XADataSource

Ping via the Glassfish admin console succeeds, but call to analysisService.getAllAnalysisTypes() now throws an exception:

Caused by: javax.ejb.TransactionRolledbackLocalException: Exception thrown from bean; nested exception is: Exception [TOPLINK-4002] (Oracle TopLink Essentials - 2.1 (Build b60e-fcs (12/23/2008))): oracle.toplink.essentials.exceptions.DatabaseException
Internal Exception: java.sql.SQLException: Error in allocating a connection. Cause: javax.transaction.SystemException

Any ideas?