yes... all custom controls are implemented with .NET. I've never tested those controls with ASP.NET but i thought that this would be possible without any problems But that's not so important for me because right now i've no plans to use ASP.NET

It's not easy for me to understand how this could work... the business layer should not refer to any outside dll. All entity definitions (typed datasets) and the methods to operate (read, update etc) on those datasets are implemented in a dll. Those dll's have to be used on the one hand by the business layer (which only contains rules and validation) and on the other hand by the dll which contains the forms because there the methods 'datasetToForm' and 'FormToDataset' are implemented.

This is how i want to split my 'thick client':

presentation layer:
- GUI

business layer:
- business rules / validation
- business entity definitions and operations
- error handling
- cryptography handling
- DB and BLOB handling
- reporter handling
etc.

data layer:
- SQL-Server

Nevertheless this is not a 'clean' implementation of a n-Tier application i will try to do it that way (if possible) because it fits my needs.

Thank you Edneeis for your help