null pointer exception on web services

I'm facing this issue when calling to a web services. Pls how to solve it.

AxisFault faultCode: {http://schemas.xmlsoap.org/soap/envelope/}Server.userException faultSubcode: faultString: java.lang.NullPointerException faultActor: faultNode: faultDetail: {http://xml.apache.org/axis/}stackTrace: java.lang.NullPointerException at java.util.Hashtable.put(Hashtable.java:396) at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl.setProperty(SAXParserImpl.java:395) at weblogic.xml.jaxp.WebLogicSAXParser.setProperty(WebLogicSAXParser.java:117) at weblogic.xml.jaxp.RegistrySAXParser.setProperty(RegistrySAXParser.java:117) at org.apache.axis.encoding.DeserializationContextImpl.parse(DeserializationContextImpl.java:246) at org.apache.axis.SOAPPart.getAsSOAPEnvelope(SOAPPart.java:538) at org.apache.axis.Message.getSOAPEnvelope(Message.java:376) at org.apache.axis.transport.http.HTTPSender.readFromSocket(HTTPSender.java:675) at org.apache.axis.transport.http.HTTPSender.invoke(HTTPSender.java:128) at org.apache.axis.strategies.InvocationStrategy.visit(InvocationStrategy.java:71) at org.apache.axis.SimpleChain.doVisiting(SimpleChain.java:150) at org.apache.axis.SimpleChain.invoke(SimpleChain.java:120) at org.apache.axis.client.AxisClient.invoke(AxisClient.java:180) at org.apache.axis.client.Call.invokeEngine(Call.java:2564) at org.apache.axis.client.Call.invoke(Call.java:2553) at org.apache.axis.client.Call.invoke(Call.java:2248) at org.apache.axis.client.Call.invoke(Call.java:2171) at org.apache.axis.client.Call.invoke(Call.java:1691) 

Thanks in Advance..