The return structure of BulkAssociatedIdEnumerator with Name '{0}' on Entity (External Content Type) with Name '{1}' and ...

The return structure of BulkAssociatedIdEnumerator with Name '{0}' on Entity (External Content Type) with Name '{1}' and Namespace '{2}' is too complex. Only one collection is allowed between the root of the return structure and TypeDescriptors which define Identifiers.