java.lang.NoClassDefFoundError-Con't find the Class in the same package?

[Yunming . Li]

I've put a class struecture into  Tomcat4_home/webapps/jds/WEB-INFO/classes

the structure is:

--classes (file: Find.class)
   --com
        --fis
            --controller (Controller.class, Composer.class)

in Find.java:
import com.fis.Controller.*;
...
protected Controller controller =null;
...
controller = new Controller(...);


in Composer.java, 
package com.fis.Controller;
Hi,
I can't figure it out what is happening. please help.

in Controller.java:
package com.fis.Controller;

private com.fis.Controller.Composer _composer = null;
//Controller constructor:
{
        _composer = new com.fis.Controller.Composer(..., ...); # ERROR LINE
(line 104)
..
}

java.lang.NoClassDefFoundError: org/apache/xerces/dom/DOMExceptionImpl at
com.fis.Controller.Controller.(Controller.java:104) at
Find.init(Find.java:54) 
...



My Qestion is :
Why the NoClassDefFoundError? the Controller.class and Composer.class is in
the same package!


Thank you very much.