the issue that was addressed in BUG ID 167175 can be recreated in netbeans 7.1.1 :

1. In netbeans 7.1.1 connect to an embedded derby database in services window
2. grab structure of a table. save it.
3. disconncet and reconnect again. you will see the tables and view the data.
4. try to grab the table structure again. Save location window opens. May warn you of existing file. then try to save.
5. you get "Unable to grab table. java.sqlNonTransientConnectionException: No current connection"
6. Restart the IDE. You can grab and save but if you disconnect and reconnect you can see the data and do SQL commands but cannot grab table.

this is the persistence.xml file:
<properties>
      <property name="hibernate.archive.autodetection" value="class"/>
      <property name="hibernate.format_sql" value="false"/>
      <property name="hibernate.show_sql" value="false"/>
      <property name="hibernate.dialect" value="org.hibernate.dialect.DerbyDialect"/>
      <property name="javax.persistence.jdbc.url" value="jdbc:derby:c:/MyDB/MyDB/"/>
      <property name="javax.persistence.jdbc.password" value="******"/>
      <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.EmbeddedDriver"/>
      <property name="javax.persistence.jdbc.user" value="nbuser"/>
      <property name="hibernate.hbm2ddl.auto" value="update"/>
    </properties>