Axis2 on oc4j problem

[Anand das]

I have developed axis2 webservices and deployed on oc4j 10.1.3. when i login to axis2 console and look for services ,I can see them
The problem is these services work when I call thru client. On the Axis2 console when i click on the service , first time it opens the wsdl on the browser
but after sometime when i try to see this wsdl by clicking on service it says "Internal server error", When i see the logs it shows

[INFO] getData request failed for dialect, http://schemas.xmlsoap.org/wsdl/
javax.xml.transform.TransformerFactoryConfigurationError: Provider net.sf.saxon.TransformerFactoryImpl could not be instantiated: java.lang.NullPointerException
at javax.xml.transform.TransformerFactory.newInstance(TransformerFactory.java:109)
at

I tried finding from forums but couldn't see any solution. The only temporary solution I found is re-start the instance and then i can see the wsdl.
Can somebody explain what's wrong? Is it oc4j or axis2?
Thanks