What type of detergent must I use in the WFW9200SQ, and what happens if I use the wrong kind?

You must use only High Efficiency (HE) detergent, identifiable by the 'HE' or 'High Efficiency' marking on the package. Using regular non-HE detergent will create too much sudsing, likely resulting in washer errors, longer cycle times, and reduced rinsing performance. It may also cause component failures and noticeable mold or mildew. (Page 11)