What would this be?

java.lang.NoClassDefFoundError: EDU/oswego/cs/dl/util/concurrent/LinkedQueue
at
org.firebirdsql.pool.PooledConnectionQueue.<init>(PooledConnectionQueue.java
:53)
at
org.firebirdsql.pool.PooledConnectionQueue.<init>(PooledConnectionQueue.java
:97)
at
org.firebirdsql.pool.AbstractConnectionPool.getQueue(AbstractConnectionPool.
java:175)
at
org.firebirdsql.pool.FBConnectionPoolDataSource.getPooledConnection(FBConnec
tionPoolDataSource.java:251)
at
org.firebirdsql.pool.FBWrappingDataSource.getConnection(FBWrappingDataSource
.java:127)
at br.com.lib.B.getConexaoSis(B.java:179)
at br.com.modulos.modOrcamento.<init>(modOrcamento.java:45)
at br.com.lib.Menus$9.actionPerformed(Menus.java:244)
at
javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1764)
at
javax.swing.AbstractButton$ForwardActionEvents.actionPerformed(AbstractButto
n.java:1817)
at
javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:4
19)
at
javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:257)
at javax.swing.AbstractButton.doClick(AbstractButton.java:289)
at
javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1113)
at
javax.swing.plaf.basic.BasicMenuItemUI$MouseInputHandler.mouseReleased(Basic
MenuItemUI.java:943)
at java.awt.Component.processMouseEvent(Component.java:5134)
at java.awt.Component.processEvent(Component.java:4931)
at java.awt.Container.processEvent(Container.java:1566)
at java.awt.Component.dispatchEventImpl(Component.java:3639)
at java.awt.Container.dispatchEventImpl(Container.java:1623)
at java.awt.Component.dispatchEvent(Component.java:3480)
at
java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:3450)
at
java.awt.LightweightDispatcher.processMouseEvent(Container.java:3165)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3095)
at java.awt.Container.dispatchEventImpl(Container.java:1609)
at java.awt.Window.dispatchEventImpl(Window.java:1590)
at java.awt.Component.dispatchEvent(Component.java:3480)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:450)
at
java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.ja
va:197)
at
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java
:150)
at
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:144)
at
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:136)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:99)

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