Etudes reports:
...that was a bug (attribute changes related to Java 7). It has been fixed in the latest Mneme 2.1.36 that we released last week. You can get it here: http://etudes.org/help/developers/mneme/download/

I tried to comment the redundant xmlns element but it seems to make no difference and could not able to import the QTI to Sakai. Strange thing is i didn't see the exception in my local instance even before commenting the redundant information.

public Element createManifest(Document doc)
{
Element root = doc.createElementNS("http://www.imsglobal.org/xsd/imscp_v1p1", "manifest");
root.setAttribute("xmlns:imsqti", "http://www.imsglobal.org/xsd/imsqti_v2p1");
root.setAttribute("xmlns:imsmd", "http://www.imsglobal.org/xsd/imsmd_v1p2");
//root.setAttribute("xmlns", "http://www.imsglobal.org/xsd/imscp_v1p1");
root.setAttribute("identifier", "Manifest-" + getUUID());
return root;
}

The QTI export file miserably fails validation (http://validator.imsglobal.org/) in this and other respects. Funny how Test Center can't import it's own export though. If this one problem with the duplicate xmlns attribute fixes the problem, it might be easy to fix – otherwise it's a black whole we might not want to make a high priority.