I would recommend approaching your problem by thinking of the RSS feed events and the features you want to write out to a feature service as two separate sets of events with different schemas (e.g. different geoevent definitions). You will want to use a Field Mapper processor element to select fields from the input you want sent to the output. There is some discussion on why you want to use this approach in the draft of the RSS tutorial I posted to the RSS" rel="nofollow" target="_blank">http://forums.arcgis.com/threads/91551-RSS-problem]RSS problem forum thread.
You should allow the RSS adapter, part of the Input connector configured to poll the specified RSS feed, to create an event definition based on its discovery of the event schema. Don�??t edit this event definition �?? instead plan on mapping fields from it to the schema of a feature service you will publish. I�??m attaching a PDF which shows the REST service specification for the feature service I published to accept data from the http://www.p4.no/rss/trafikk.aspx data feed. Note in particular that the feature service has only the Title, PubDate, and Link fields from the feed. I�??m not sure what field you were using for the "description". You should create the feature service then import its event definition; don't try to create a single event definition which will satisfy both the Input and the Output.
I�??ve attached a second PDF which shows what a simple GeoEvent Service, using a Field Mapper to map fields from the incoming RSS to the target feature service should look like.
Here�??s a screenshot of a basic web map consuming the feature service being updated from the RSS feed. [ATTACH=CONFIG]29188[/ATTACH]
