MSB3645: No se encuentra .NET Framework v3.5 Service Pack 1. Para establecer el destino en "X", debe estar instalado .NET Framework v3.5 Service Pack 1 o una versión posterior.
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English version
MSB3645: .NET Framework v3.5 Service Pack 1 was not found. In order to target "X", .NET Framework v3.5 Service Pack 1 or later must be installed.