ssrs: "unknown collection member" when I try show or hide a rectangle based in a expression

I get the error "unknown collection member" when I try show or hide a rectangle (contains some tables) based in this expression:

= First(Fields!Modalidad.Value, "ModalidadSubmodalidad")<>"Distancia"

Reference is generated automatically (dataset exists and field exist开发者_如何学编程s)

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Álvaro, try adding a tablix to your report. Link the tablix to your dataset then add your image component to the tablix.