javadoc produces strange error

When I run javadoc I get this error...>javadoc C:\ GUIManager.javaException in thread "main" java.lang.NoClassDefFoundError: com/sun/tools/javadoc/Mainanyone any ideas?
[206 byte] By [PWils05a] at [2007-10-2 12:41:47]
# 1
http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/javadoc.html#runningjavadoc
MartinHilperta at 2007-7-13 9:47:06 > top of Java-index,Developer Tools,Debugging and Profiling Tool APIs...