Scanning with TWAIN

[Marman]

Hello

I am making an application to scan with TWAIN. I can get to state 4 OK, and scan with the UI. But I need to hide the UI. When I do this the scanner does nothing. I believe it needs some capabilities set (like height and width). So I try to get the physical height and width so I can set them. Herein lies the problem. I get 18874402 back for the physical height and width. (neither can I get the units). I get RC=SUCCESS. I don't think it could be a signed/unsigned issue because what boundary is at 18 million +/- with whatever units? I tried some other code I found but that returns 0. I can't figure out what I am doing wrong. Here's the code:

    Private Function GetOneValue(ByVal twCapability As twsCapability) As String

        Dim rc As twRC
        Dim strTemp As String
        Dim twOneValue As TW_ONEVALUE


        rc = DS_Capability(mtwApp, mtwSource, twDG.Control, twDAT.Capability, twMSG.Get, twCapability)
        If rc = twRC.Success Then
            strTemp = vbNullString
            Select Case twCapability.ConType
                Case twContainerTyoe.One
                    twOneValue = New TW_ONEVALUE
                    Marshal.PtrToStructure(twCapability.Handle, twOneValue)
                    strTemp = CType(twOneValue.Item, String)
                Case Else
                    MsgBox("Error, one value expected; " & twCapability.ConType & " returned.")
            End Select
            Marshal.FreeHGlobal(twCapability.Handle)
            Return strTemp
        Else
            ErrorStatus()
            Return vbNullString
        End If

    End Function

And here's how I call it:

            twCapability = New twsCapability
            With twCapability
                .Cap = twCap.IPhysicalWidth
                .ConType = twContainerTyoe.One   'TWON_DONTCARE16
                '.Handle = Nothing
            End With
            strWidth = GetOneValue(twCapability)

If I can get it to work I will post the class here for others to use. Any help is appreciated, thanks for looking.