When I follow this walkthrough for External Content type
I am not able to register the ECT in SPD with the following error
This operation is based on a method with complex data types in its signature. To be supported, each complex type referenced in the method signature must have a default constructor that does not require any parameters. Update the .NET connectivity assembly code and redeploy it to the Business Connectivity Services before retrying."
Then I change the class IEnumerable for List class and it works I am able to see the ECT in SPD
what is the difference between them?