XML restriction violated: Element must be empty

If you get an error of the form:

XML restriction is violated/XML restriccion es violada: Element [cfdi:Traslados/cfdi:Traslado] must be empty/El elemento debe estar vacio.

cvc-complex-type.2.1: Element 'cfdi:Traslado' must have no character or element information item [children], because the type's content type is empty.

This is because extra whitespace has been added inside an element that must be empty. For example,

<cfdi:Traslado Base="2250000" Impuesto="002" TipoFactor="Tasa" TasaOCuota="1.600000" Importe="360000">
  </cfdi:Traslado>

has white space after the end of the opening tag > and before start of the closing tag </cfdi:Traslado>, but the element must be empty. The correct form should be

<cfdi:Traslado Base="2250000" Impuesto="002" TipoFactor="Tasa" TasaOCuota="1.600000" Importe="360000"></cfdi:Traslado>

FirmaSAT will never produce output with that error (unless it's there in the first place). Do not attempt to reformat or "prettify" the XML output after signing.