Deinstalling/reinstalling does not work in 3.61

Hi there,
having problems on ErlWood nodes and willing to remove the actual version and install an older ones, I came across the problem that Help>About Knime …> Installation Details>Update did not provide ERlWood nodes as possible updates (even reinstalling) after I had removed them through the same means and restarted.
Is this ok? I don’t think so… then using “install new software” (from nightly trunk only ErlWood nodes)
I got this:
An error occurred during the org.eclipse.equinox.internal.p2.engine.phases.CheckTrust phase.
session context was:(profile=KNIMEProfile, phase=org.eclipse.equinox.internal.p2.engine.phases.CheckTrust, operand=, action=).
Error reading signed content.
Exception in opening zip file: C:\Program Files\KNIME\plugins\org.erlwood.knime.cheminformatics_3.3.0.v201701271216


PS I am running KNIME behind a company firewall that did not provide any problems in the past. knime.ini uses -clean.