Cannot install Mylyn connector from central - failure blocks other plugin installs

After installing this plugin from Central:

Mylyn Tasks Connector: Bugzilla 3.9.0.I20130319-0842 org.eclipse.mylyn.bugzilla_feature.feature.group

After eclipse restarts, accessing Central raises this error: An internal error occurred during:

"Update project wizard list". org.eclipse.mylyn.commons.core.CoreUtil.newXmlReader()Lorg/xml/sax/XMLReader;

And any attempt to install additional plugins fail with the same error: Unexpected exception:

org.eclipse.mylyn.commons.core.CoreUtil.newXmlReader()Lorg/xml/sax/XMLReader; org.eclipse.mylyn.commons.core.CoreUtil.newXmlReader()Lorg/xml/sax/XMLReader; org.eclipse.mylyn.commons.core.CoreUtil.newXmlReader()Lorg/xml/sax/XMLReader; org.eclipse.mylyn.commons.core.CoreUtil.newXmlReader()Lorg/xml/sax/XMLReader;