Hi,
The first thing to do to start diagnosing this problem is to turn on some logging.
In your persistence.xml, add the following to the properties element:
<property name="toplink.logging.level" value="FINEST"/>
When you have done that, take a look at your logs. There should be some information that shows how TopLink Essentials is logging into the database. It should include a URL and a username. Check to make sure those correspond to what you expect.
If that does not help, is it possible to post a persistence.xml that reproduces the problem and the snippet of code the leads up to your exception.
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