I have implemented SagePay payment based on the .Net integration kit supplied by SagePay.
All works fine but when I enable the 3D Secure and choose a non-3D secure card I get this exception:
"Requested value 'NOTAVAILABLE' was not found" | Boolean TryParseEnum(System.Type, System.String, Boolean, EnumResult ByRef)
That exception occurs in the method GetServerNotificationRequest() on the SagePayIntegration class within the assembly SagePay.IntegrationKit.DotNet.dll.
NOTE: I already tried this solution SagePay .Net Integration Kit - Error when returning NOTAVAILABLE value for 3dSecureStatus but didn't work for me.