error in searching extensions

Why can’t I install the Extension: LigandScout Extensions for the KNIME Workbench? It has the error “HTTP Server ‘Internal Error’: https://hub.knime.com/inteligand/extensions/com.inteligand.knime/latest/content.xml
HTTP Server ‘Internal Error’: https://hub.knime.com/inteligand/extensions/com.inteligand.knime/latest/content.xml
HttpComponents connection error response code 500.”

Just I want to know the reason and how I need to do. Thank you!