Remember you are using version 4.0.1 in the Adobe S1000D app pack. It would therefore be a good idea to use the same version of the S1000D specification to guide your use of S1000D. However in this case the answer is that you are trying to insert the dmRef in the wrong location. It should be a child of the applicCrossRefTableRef element. In your screenshot the insertion point is in the displayText element.