He estado buscando en la web durante las últimas horas, encontrando mucha información relacionada con mi problema, pero en realidad ninguno los solucionó.

Mi máquina es de 64 bits con un Visual Studio 10 de 32 bits instalado. La solución usa .Net 4. La solución incluye la instalación de 64 bits de Crystal Reports. La solución también incluye log4net.

La compilación del proyecto en VS2010 está bien tanto para Debug como para Release, cualquier CPU.

He agregado un proyecto de configuración web que quiero construir. Sin embargo, sin importar la configuración, obtengo los siguientes errores al compilar (tanto dentro de la interfaz de usuario de VS como en la línea de comandos usando devenv.exe):

ERROR: File 'CrystalDecisions.ReportAppServer.Prompting.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.Prompting.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.ObjectFactory.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.ObjectFactory.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.XmlSerialize.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.XmlSerialize.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.CommonObjectModel.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.CommonObjectModel.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.CommonControls.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.CommonControls.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.ReportDefModel.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.ReportDefModel.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'log4net.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'log4net.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.Controllers.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.Controllers.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.DataDefModel.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.DataDefModel.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.CubeDefModel.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.CubeDefModel.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.ClientDoc.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.ClientDoc.dll' targeting 'x64' is not compatible with the project's target platform 'x86'
ERROR: File 'CrystalDecisions.ReportAppServer.CommLayer.dll' targeting 'AMD64' is not compatible with the project's target platform 'x86'
WARNING: File 'CrystalDecisions.ReportAppServer.CommLayer.dll' targeting 'x64' is not compatible with the project's target platform 'x86'

He intentado establecer explícitamente la configuración de los proyectos en x86 y x64, sin ningún cambio.

¿Puede alguien guiarme por el camino correcto?

Edit: captura de pantalla agregada que muestra que no puedo elegir la plataforma para el proyecto de configuración.