Problem Starting software

I get the following error when trying to start the software. It ran fine a month or two ago on ubuntu 7.04 and then i havent used it since today, now on ubuntu 7.10

Exception in thread "RepRap" java.lang.NoClassDefFoundError: javax/vecmath/Tuple3d
at org.reprap.Main.createAndShowGUI(Unknown Source)
at org.reprap.Main.access$2400(Unknown Source)
at org.reprap.Main$23.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)

anyone know how I can fix this error?

Thanks,
Mike

now I'm getting...

Exception in thread "RepRap" java.lang.NoClassDefFoundError: org/j3d/renderer/java3d/loaders/STLLoader
at org.reprap.gui.STLObject.(Unknown Source)
at org.reprap.gui.RepRapBuild.createSceneBranchGroup(Unknown Source)
at org.reprap.gui.Panel3D.initJava3d(Unknown Source)
at org.reprap.gui.Panel3D.initialise(Unknown Source)
at org.reprap.gui.RepRapBuild.(Unknown Source)
at org.reprap.Main.createAndShowGUI(Unknown Source)
at org.reprap.Main.access$2400(Unknown Source)
at org.reprap.Main$23.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)

[forums.reprap.org]

that fixed my problem! I was downloading the jar file as a html file.