primero
Web.Config/system.web/httpRuntime/maxRequestLength
Unidad de medida: kilobytes
Valor predeterminado 4096 KB (4 MB)
Max. valor 2147483647 KB (2 TB)
Segundo Web.Config/system.webServer/security/requestFiltering/requestLimits/maxAllowedContentLength (en bytes)
Unidad de medida: bytes
Valor predeterminado 30000000 bytes (28.6 MB)
Max. valor 4294967295 bytes (4 GB)
Ejemplo:
<system.web>
<!--The default size is 4096 kilobytes (4 MB). MaxValue is 2147483647 KB (2 TB)-->
<!-- 100 MB in kilobytes -->
<httpRuntime maxRequestLength="102400" />
</system.web>
<system.webServer>
<security>
<requestFiltering>
<!--The default size is 30000000 bytes (28.6 MB). MaxValue is 4294967295 bytes (4 GB)-->
<!-- 100 MB in bytes -->
<requestLimits maxAllowedContentLength="104857600" />
</requestFiltering>
</security>
</system.webServer>
Salusos.