i installed jython in win2k after failed times because of two things needed to be done:  lauching jython.class with completed java.exe path(i don't know the reason fully), the other is adding jython.jar to classpath.
 
About your problem, i can't think out any other reasons except  of the absense of jython.jar  in your classpath.  but i'm not familar with linux, so check it youself please. wish it be helpful.
 
regards
 
     lee
 
 

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