How to call .NET 3.0 dll from .NET 1.1 application?

Question

We have a legacy .NET 1.1 appliation which communicates multiple systems along with SAP systems also. Currently we are using DCOM connectorfor SAP communication. We have decided to replace the DCOM connector with .NET 3.0 SAP connector as latest SAP versions are not providing support for the DCOM connector. But the problem is we can not call .NET 3.0 dll from .NET 1.1 dll.

We are considered the below options.

(1) Migrating current 1.1 application to 3.5 or latest. However we didn't get approval for this since it consumes huge effort as the application is critical and complex
(2) Create Intermediate VB component which can act as communicator for both 1.1 and 3.5. It adds one more layer and leads to architectural change. We didn't get approval for this also due to performance issues and architectural review.
(3) Create a web-service which calls SAP through .NET SAP connector and host in the same server and consume that from .NET 1.1 application. This also not get approved due to performance issues and architectural review.
(4)Checking any other mechanism in WCF which helps to communication between .NET 1.1 and .NET 3.0 applications. This also not get approved due to performance issues and architectural review.
(5) Make .NET 3.5 classes exposed as COM objects (out-of-process), and use these COM objects from your .NET 1.1 app. We have tried this option and it is giving the exception "A reference to 'NETDLL' could not be added. Converting the type library to a .NET assembly failed. Type library NETDLL was exported from a CLR assembly and cannot be re-imported as a CLR assembly"

Can you help me any other approaches which doesn't cost architectural change and doesn't cause performance hit. Please help

Answer 1

Finally we have resolved the issue with the following approach. We have decided to use .NET 2.0 SAP connector for 1.1 applications. We can integrate or configure the .NET 2.0 connector with .NET 1.1 IDE which Visual studio 2003. Once we integrate it to visual studio 1.1 IDE we can create 1.1 SAP 2.0 connector project where you can consume .NET 2.0 SAP connector in your 1.1 project which generates .NET 1.1 dll.

Answer 2

I've had a similar task long time ago.
Probably the easiest way is to make your .NET 3.5 classes exposed as COM objects (out-of- process), and use these COM objects from your .NET 1.1 app.