NullPointer while reading XMI

Hello,

I get a NullPointerException when I execute a transformation. I'm not sure
if this is a problem with ATL or with my ecore model, but maybe someone had
this exception too and can give me a clue.
I am quite confused, because I used the editor generated from the metamodel
to create the input model. The editor can read this model again.

The code at the point of the exception is:
EFactory eFactory = eDataType.getEPackage().getEFactoryInstance();
and "getEPackage()" returns null eventually.

Thanks for any clue!
Nicolas

---
Trying to connect to remote debuggee
java.lang.NullPointerException
	at
org.eclipse.emf.ecore.xmi.impl.XMLHelperImpl.setValue(XMLHelperImpl.java:876
)
	at
org.eclipse.emf.ecore.xmi.impl.XMLHandler.setFeatureValue(XMLHandler.java:17
52)
	at
org.eclipse.emf.ecore.xmi.impl.XMLHandler.setAttribValue(XMLHandler.java:181
1)
	at
org.eclipse.emf.ecore.xmi.impl.SAXXMIHandler.handleObjectAttribs(SAXXMIHandl
er.java:147)
	at
org.eclipse.emf.ecore.xmi.impl.XMLHandler.createObjectFromFactory(XMLHandler
.java:1353)
	at
org.eclipse.emf.ecore.xmi.impl.XMLHandler.createObjectByType(XMLHandler.java
:733)
	at
org.eclipse.emf.ecore.xmi.impl.XMLHandler.createTopObject(XMLHandler.java:74
4)
	at
org.eclipse.emf.ecore.xmi.impl.XMLHandler.processElement(XMLHandler.java:447
)
	at
org.eclipse.emf.ecore.xmi.impl.XMIHandler.processElement(XMIHandler.java:65)
	at
org.eclipse.emf.ecore.xmi.impl.XMLHandler.startElement(XMLHandler.java:434)
	at
org.eclipse.emf.ecore.xmi.impl.SAXWrapper.startElement(SAXWrapper.java:75)
	at org.apache.crimson.parser.Parser2.maybeElement(Unknown Source)
	at org.apache.crimson.parser.Parser2.parseInternal(Unknown Source)
	at org.apache.crimson.parser.Parser2.parse(Unknown Source)
	at org.apache.crimson.parser.XMLReaderImpl.parse(Unknown Source)
	at javax.xml.parsers.SAXParser.parse(Unknown Source)
	at
org.eclipse.emf.ecore.xmi.impl.XMLLoadImpl.load(XMLLoadImpl.java:129)
	at
org.eclipse.emf.ecore.xmi.impl.XMLResourceImpl.doLoad(XMLResourceImpl.java:1
60)
	at
org.eclipse.emf.ecore.resource.impl.ResourceImpl.load(ResourceImpl.java:970)
	at
org.atl.engine.repositories.emf4atl.ASMEMFModel.loadASMEMFModel(ASMEMFModel.
java:155)
	at
org.atl.eclipse.engine.AtlEMFModelHandler.loadModel(AtlEMFModelHandler.java:
67)
	at
org.atl.eclipse.adt.launching.AtlLaunchConfigurationDelegate.getModelInput(A
tlLaunchConfigurationDelegate.java:251)
	at
org.atl.eclipse.adt.launching.AtlLaunchConfigurationDelegate.runAtlLauncher(
AtlLaunchConfigurationDelegate.java:171)
	at
org.atl.eclipse.adt.launching.AtlLaunchConfigurationDelegate.runAtlLauncher(
AtlLaunchConfigurationDelegate.java:147)
	at
org.atl.eclipse.adt.launching.AtlLaunchConfigurationDelegate.runAtlLauncher(
AtlLaunchConfigurationDelegate.java:130)
	at
org.atl.eclipse.adt.launching.AtlLaunchConfigurationDelegate.runAtlLauncher(
AtlLaunchConfigurationDelegate.java:112)
	at
org.atl.eclipse.adt.launching.AtlLaunchConfigurationDelegate.access$0(AtlLau
nchConfigurationDelegate.java:101)
	at
org.atl.eclipse.adt.launching.AtlLaunchConfigurationDelegate$1.run(AtlLaunch
ConfigurationDelegate.java:79)
Connected.