I noticed that the problem was my environment.
I'm using 2 different schemas but my users have access to both of them.
This runs fine to select, but for non-idempotent operations it does not work.
is your problem solved? Are you using a JEE container?
If you use:
in components.xml, Seam will ask the container to create a transaction. Therefore you can see Seam is managing the transaction lifecycle (begin, commit/rollback) but delegates the actual creation of the transaction to the container.
That container transaction should allow XAResources join the current tx if your container is using a JTA tx manager.
Then it's just a matter of configuring your different XA datasources and bind them to their respective PU.