Oscilloscope might not start due to a number of different problems.  Let's try to debug:

1.  Is your tinyos-1.x/tools/java directory in your matlab Classpath.txt file?  Go back to "Step 1:  Change your Matlab classpath" in the tutorial and be sure this is typed in correctly.  To test if it is correct, try typing

methods net.tinyos.oscope.oscilliscope

If you get a list of the methods of this class, the class can be found by matlab.  Otherwise, it is probably a classpath problem.

2.  If Matlab can start Oscilloscope but not data is drawn, it might be one of two problems. 

    a.  Make sure that you have an instance of SerialForward running.  Make sure it is serving on port 9000 by looking at the GUI.

    b.  Make sure that data is coming in from the oscilloscopeRF mote.  Look at your SerialForward GUI and see if the number of packets received is increasing.  If it is, try running ForwarderListen to make sure that the packets are really of the OscopeMsg format.