V2.1 update site problems


I am using KNIME 2.1 in the development environment. I am located behind a proxy that I set up using the preference settings. When I start KNIME (with or without having the expert modus enabled) I was able to use the update site to retrieve most of the extensions.
some are missing though. Most notably R and chemistry nodes. When I now try to expand the “KNIME & Extensions Update Site” under File->Update KNIME I get the following error message:

An internal error occurred during:“Fetching children of KNIME & Extensions Update Site” java.lang.NullPOinterException

When selecting the “include items that have already been installed” I see R statistics integration. But they are not in the plugins directory nor can I see them from within KNIME…

Any clue of what might be going wrong?