Cannot complete the install because one or more required items could not be found.
Software being installed: Selenium for KNIME 1.0.0.201511131527 (ws.palladian.nodes.selenium.feature.feature.group 1.0.0.201511131527)
Missing requirement: Selenium for KNIME 1.0.0.201511131527 (ws.palladian.nodes.selenium 1.0.0.201511131527) requires 'bundle org.knime.workbench.core [2.11.0,3.0.0)' but it could not be found
Cannot satisfy dependency:
From: Selenium for KNIME 1.0.0.201511131527 (ws.palladian.nodes.selenium.feature.feature.group 1.0.0.201511131527)
To: ws.palladian.nodes.selenium [1.0.0.201511131527]
which KNIME version are you running on? I assume 3.0? The currently available public beta versions only support 2.x. ([edit] whoops, sorry, the title stated the obvious).
I'll try to provide a 3.0-compatible version asap, in fact it is already finished. In the meantime however until its available, you need to use 2.x. Sorry for any invonvenience caused.