Key subfield for keyed data structure array must not be a data structure or an array.
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Cause . . . . . : A qualified name in the form DS_ARRAY(*).KEY must have a scalar subfield as the key. The statement is ignored.
Recovery . . . : If the key is an array subfield, then add indexing for the array. If the key is a data structure subfield, then add further subfields to the qualified name. Compile again.