I am using a the Data Access application block within a Windows Workflow (done in VS2005) in SharePoint. I'm getting the follwing error:

Object reference not set to an instance of an object.

...and the source is

Microsoft.Practices.EnterpriseLibrary.Data

NB* All the solution assemblies have been added to GAC.

I'm thinking the error is being caused by the absence of the app.config file somewhere where the assemblies in GAC would look for it.
Anyone knows how to solve this?