C# pass/return bitmap to VB6

Hi I successfully created a c# dll that can be called from VB6. However I dont understand why I can do (after adding dll as a reference)... Dim a As New Calc msgbox.Show = MsgBox a.Add(100, 100) 'dll returns x*y so a function that returns an integer works but a function that returns a bitmap does not. Dim a As New Calc Picture2 = a.getpic(LoadPicture(App.Path & "\images\desktop2.bmp)) 'c# dll that returns bmp picture1.picture = picture 2 IT SAYS TYPE MIS_MATCH WHEN I DO THIS. WHY??????????????????????????? PLEEEEEEEEEESE HEELLLLP.