Posting code on this would make it even more confusing. Heres the basic problem again. The problem isnt code specific.
Each of the 4 BOs (all of which are in different business projects and have slightly different data/entities)
Have a Get EntityListbyDLN method that returns and entite list of DataCaptureEntity (the entity is specific to that businness project).

Heres an example:

Public Function GetEntityListbyDLN(ByVal DLN As Int64) As mmBindingList(Of DataCaptureReturnEntity)
Return Me.EntityList
End Function
This same method call exists in all four business projects DataCap business object. Each one of the DataCaptureReturnEntity in mmBindingList is specific to its DataCap business object.
Follow so far?

Each of the 4 BO’s implement and interface from a baselib project
IdataCap . I want a method signature on that interface to be implemented on all 4 BO’s for the GetEntityListbyDLN function.
So it would looks something like this

Public interface IDataCap
Function GetEntityListbyDLN(ByVal DLN As Int64) As mmBindingList(Of “SOMETHING”)
End Interface

The problem is that no matter what I try using in place of “SOMETHING”
I cant get it to work on the BO’s end.