quando compilo il build.xml mi esce questo errore


Buildfile: D:\Universita\Web Service\esempio\build.xml
init:
pre.compile.test:
[echo] Stax Availability= true
[echo] Axis2 Availability= true
compile.src:
[javac] Compiling 1 source file to D:\Universita\Web Service\esempio\build\classes
[javac] D:\Universita\Web Service\esempio\src\org\example\www\esempio\PWCBHa ndler.java:2: package org.apache.ws.security does not exist
[javac] import org.apache.ws.security.WSPasswordCallback;
[javac] ^
[javac] D:\Universita\Web Service\esempio\src\org\example\www\esempio\PWCBHa ndler.java:18: cannot find symbol
[javac] symbol : class WSPasswordCallback
[javac] location: class org.example.www.esempio.PWCBHandler
[javac] WSPasswordCallback pwcb = (WSPasswordCallback)callbacks[i];
[javac] ^
[javac] D:\Universita\Web Service\esempio\src\org\example\www\esempio\PWCBHa ndler.java:18: cannot find symbol
[javac] symbol : class WSPasswordCallback
[javac] location: class org.example.www.esempio.PWCBHandler
[javac] WSPasswordCallback pwcb = (WSPasswordCallback)callbacks[i];
[javac] ^
[javac] 3 errors

BUILD FAILED
D:\Universita\Web Service\esempio\build.xml:43: Compile failed; see the compiler error output for details.

Total time: 2 seconds

quale potrebbe essere il problema?