First I built successfully. After that, I got the following error information and the ant teminated.

Who can help me find out some clues? Thanks so much!

[] Could not load definitions from resource org/apache/tools/ant/antlib.xml. It could not be found.
[hibernatetool] Executing Hibernate Tool with a Standard Configuration
[hibernatetool] 1. task: hbm2java (Generates a set of .java files)
[hibernatetool] 2010-3-21 19:19:24 org.hibernate.cfg.Environment <clinit>