HTTP 502 with TIBCO Knime Nodes


We're looking into an integration of Knime ad Tibco Spotfire. For this I've loaded the three TIBCO Spotfire nodes (File Writer, File Reader, Information Link Reader) into my Knime environment. Using File Writer I can successfully write an sbdf File into the Spotfire Library. However, using the same server information, File Reader and Information Lnk Reader return an http status 502 (Bad Gateway). Any idea what could cause this?