I'm not able to update the original submission with the previous content.
I past the content, click on submit, there is something in progress but no update and no logs

Hum it seems that original submission was cleared.
But I don't know if I made a mistake

I think it would be quicker to fix it in the connector directly. I have contributed a fix and released a new build.
http://sbegaudeau.github.io/mylyn.tasks/

I have also improved the description of the feature as requested: https://github.com/sbegaudeau/mylyn.tasks/commit/a444251455d1a5613c065ad4ccf4f3e7374b1d46

If the comment or the artifact is submitted by an anonymous user, the returned id will be 0.

We can also return an AnonymousUser in this case but that would be a backward compatibility breakage

From the stack trace of the exception:
at org.tuleap.mylyn.task.internal.core.wsdl.soap.v1.CodendiAPIBindingStub.getUserInfo(CodendiAPIBindingStub.java:2815)
at org.tuleap.mylyn.task.internal.core.net.TuleapSoapConnector.getPersonFromId(TuleapSoapConnector.java:1525)
at org.tuleap.mylyn.task.internal.core.net.TuleapSoapConnector.populateArtifact(TuleapSoapConnector.java:799)

We can see that the problem comes from the retrieval of the user info. In the connector we are receiving the comments of an artifact (TuleapSoapConnector.java:799) [1]. The author of one of these comments has the id "0":
- int submittedBy = artifactComment.getSubmitted_by();

This identifier is given to us by the tracker SOAP API [2]. Then, we are asking the core SOAP API [3] for the user info for the identifier that we have received (TuleapSoapConnector.java:1525) [4]. Tuleap tells us that this identifier is invalid:
AxisFault
faultCode: 0
faultSubcode:
faultString: Invalid user id: 0
faultActor: getUserInfo
faultNode:
faultDetail:
{http://xml.apache.org/axis/}stackTrace:Invalid user id: 0

Is there a reason why an user identifier received from Tuleap (Tracker SOAP API) would be considered invalid by Tuleap (Core SOAP API)?

References:
1: https://github.com/sbegaudeau/mylyn.tasks/blob/tuleap_master/org.tuleap.mylyn.task.core/src/org/tuleap/mylyn/task/internal/core/net/TuleapSoapConnector.java#L799
2: https://demo.tuleap.net/plugins/tracker/soap/view-wsdl#op.id398250480553
3: https://demo.tuleap.net/soap/wsdl#op.id398249881351
4: https://github.com/sbegaudeau/mylyn.tasks/blob/tuleap_master/org.tuleap.mylyn.task.core/src/org/tuleap/mylyn/task/internal/core/net/TuleapSoapConnector.java#L1525

And after that synchro fails:

eclipse.buildId=M20130204-1200
java.version=1.6.0_27
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=en_US
Command-line arguments:  -os linux -ws gtk -arch x86_64

Error
Thu May 16 17:08:19 CEST 2013
Synchronization failed

java.lang.NullPointerException

<p>After having read the doc and entered the right URL it's working, thanks.</p>
<p>However, I cannot fetch all artifacts (I wanted to add a follow-up to this through eclipse but during synchro ('Default' report in 'Bugs' tracker) I get failure like:</p>
<pre>
eclipse.buildId=M20130204-1200
java.version=1.6.0_27
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=en_US
Command-line arguments: -os linux -ws gtk -arch x86_64

Error
Thu May 16 17:08:19 CEST 2013
Invalid user id: 0

AxisFault
faultCode: 0
faultSubcode:
faultString: Invalid user id: 0
faultActor: getUserInfo
faultNode:
faultDetail:
{http://xml.apache.org/axis/}stackTrace:Invalid user id: 0
at org.apache.axis.message.SOAPFaultBuilder.createFault(SOAPFaultBuilder.java:222)
at org.apache.axis.message.SOAPFaultBuilder.endElement(SOAPFaultBuilder.java:129)
at org.apache.axis.encoding.DeserializationContext.endElement(DeserializationContext.java:1087)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:604)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1759)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2915)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:625)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:116)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:488)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:819)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:748)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:123)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1208)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:525)
at javax.xml.parsers.SAXParser.parse(SAXParser.java:392)
at org.apache.axis.encoding.DeserializationContext.parse(DeserializationContext.java:227)
at org.apache.axis.SOAPPart.getAsSOAPEnvelope(SOAPPart.java:696)
at org.apache.axis.Message.getSOAPEnvelope(Message.java:435)
at org.apache.axis.handlers.soap.MustUnderstandChecker.invoke(MustUnderstandChecker.java:62)
at org.apache.axis.client.AxisClient.invoke(AxisClient.java:206)
at org.apache.axis.client.Call.invokeEngine(Call.java:2784)
at org.apache.axis.client.Call.invoke(Call.java:2767)
at org.apache.axis.client.Call.invoke(Call.java:2443)
at org.apache.axis.client.Call.invoke(Call.java:2366)
at org.apache.axis.client.Call.invoke(Call.java:1812)
at org.tuleap.mylyn.task.internal.core.wsdl.soap.v1.CodendiAPIBindingStub.getUserInfo(CodendiAPIBindingStub.java:2815)
at org.tuleap.mylyn.task.internal.core.net.TuleapSoapConnector.getPersonFromId(TuleapSoapConnector.java:1525)
at org.tuleap.mylyn.task.internal.core.net.TuleapSoapConnector.populateArtifact(TuleapSoapConnector.java:799)
at org.tuleap.mylyn.task.internal.core.net.TuleapSoapConnector.performQuery(TuleapSoapConnector.java:706)
at org.tuleap.mylyn.task.internal.core.client.TuleapClient.getSearchHits(TuleapClient.java:99)
at org.tuleap.mylyn.task.internal.core.repository.TuleapRepositoryConnector.performQuery(TuleapRepositoryConnector.java:287)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeQueriesJob.synchronizeQuery(SynchronizeQueriesJob.java:311)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeQueriesJob.synchronizeQueries(SynchronizeQueriesJob.java:268)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeQueriesJob.run(SynchronizeQueriesJob.java:201)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeRepositoriesJob.updateQueries(SynchronizeRepositoriesJob.java:186)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeRepositoriesJob.run(SynchronizeRepositoriesJob.java:142)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)

{http://xml.apache.org/axis/}hostname:belay

Invalid user id: 0
at org.apache.axis.message.SOAPFaultBuilder.createFault(SOAPFaultBuilder.java:222)
at org.apache.axis.message.SOAPFaultBuilder.endElement(SOAPFaultBuilder.java:129)
at org.apache.axis.encoding.DeserializationContext.endElement(DeserializationContext.java:1087)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:604)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1759)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2915)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:625)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:116)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:488)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:819)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:748)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:123)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1208)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:525)
at javax.xml.parsers.SAXParser.parse(SAXParser.java:392)
at org.apache.axis.encoding.DeserializationContext.parse(DeserializationContext.java:227)
at org.apache.axis.SOAPPart.getAsSOAPEnvelope(SOAPPart.java:696)
at org.apache.axis.Message.getSOAPEnvelope(Message.java:435)
at org.apache.axis.handlers.soap.MustUnderstandChecker.invoke(MustUnderstandChecker.java:62)
at org.apache.axis.client.AxisClient.invoke(AxisClient.java:206)
at org.apache.axis.client.Call.invokeEngine(Call.java:2784)
at org.apache.axis.client.Call.invoke(Call.java:2767)
at org.apache.axis.client.Call.invoke(Call.java:2443)
at org.apache.axis.client.Call.invoke(Call.java:2366)
at org.apache.axis.client.Call.invoke(Call.java:1812)
at org.tuleap.mylyn.task.internal.core.wsdl.soap.v1.CodendiAPIBindingStub.getUserInfo(CodendiAPIBindingStub.java:2815)
at org.tuleap.mylyn.task.internal.core.net.TuleapSoapConnector.getPersonFromId(TuleapSoapConnector.java:1525)
at org.tuleap.mylyn.task.internal.core.net.TuleapSoapConnector.populateArtifact(TuleapSoapConnector.java:799)
at org.tuleap.mylyn.task.internal.core.net.TuleapSoapConnector.performQuery(TuleapSoapConnector.java:706)
at org.tuleap.mylyn.task.internal.core.client.TuleapClient.getSearchHits(TuleapClient.java:99)
at org.tuleap.mylyn.task.internal.core.repository.TuleapRepositoryConnector.performQuery(TuleapRepositoryConnector.java:287)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeQueriesJob.synchronizeQuery(SynchronizeQueriesJob.java:311)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeQueriesJob.synchronizeQueries(SynchronizeQueriesJob.java:268)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeQueriesJob.run(SynchronizeQueriesJob.java:201)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeRepositoriesJob.updateQueries(SynchronizeRepositoriesJob.java:186)
at org.eclipse.mylyn.internal.tasks.core.sync.SynchronizeRepositoriesJob.run(SynchronizeRepositoriesJob.java:142)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
</pre>

I just tried on with my credential on "https://tuleap.net/plugins/tracker/?group_id=101" with the same version of Eclipse and the same version of the plugin and it worked for me. Could you please paste here the complete error message which should be available in the error log view (Window -> Show View -> Other -> Error Log) or in the log file in your Eclipse installation folder.