As you probably already know, you need to include System.Runtime.InteropServices in your .Net project and use DllImport to load the library. If you are passing parameters correctly, the function call should work the same in VB6 and .Net. If you would like to post parts of your code showing how you're trying to open the card in VB6 and in .Net, and also results in both cases, we may be able to give you some suggestions. Alternatively, you can contact us to our Support email address to discuss your requirements and how to solve the problem.