FULL PRODUCT VERSION :
java version "1.6.0-rc"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-rc-b60)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b60, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
SAXParserFactory.newInstance() throws FactoryConfigurationError if in current contextClassLoader=null. Version 1.5_04, 1.5_05 works ok. As result of this change of the behaviour, maven tool can't work under mustang.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run example

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
SAXParserFactory.newInstance() expected to use system loader when there is no context one.
ACTUAL -
Exception is thrown

ERROR MESSAGES/STACK TRACES THAT OCCUR :
C:\>java -showversion -Djaxp.debug=1 JAXPTest
java version "1.6.0-rc"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-rc-b60)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b60, mixed mode, sharing)

JAXP: find factoryId =javax.xml.parsers.SAXParserFactory
JAXP: found jar resource=META-INF/services/javax.xml.parsers.SAXParserFactory using ClassLoader: nul
l
JAXP: found in resource, value=com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl
Exception in thread "main" javax.xml.parsers.FactoryConfigurationError: Provider com.sun.org.apache.
xerces.internal.jaxp.SAXParserFactoryImpl could not be instantiated: java.lang.NullPointerException
        at javax.xml.parsers.SAXParserFactory.newInstance(Unknown Source)
        at JAXPTest.main(JAXPTest.java:8)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.xml.parsers.SAXParserFactory;

public class JAXPTest
{
 public static void main(String[] args) throws Exception
 {
  Thread.currentThread().setContextClassLoader(null);
  SAXParserFactory.newInstance();
 }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Don't set context class loader to null.

Release Regression From : 5.0u5
The above release value was the last known release where this 
bug was known to work. Since then there has been a regression.