Create Group 4 tiff

I created  a tif file using the following code but when i try to import the pages using our imaging system (UNIsys InfoImage) i get an error  Invalid format.  Invalid Tiff Format is the error i get.
 
I used the following code.  
 Dim newBitMap As New Bitmap(desiredWidth, desiredHeight)
                        Dim Grp As Graphics = Graphics.FromImage(newBitMap)
                     Grp.DrawString(docType, drawFont, Brushes.Black, 2, 2)
                      'Grp.Dispose()
                      'newBitMap.Save("C:\mergeddocs\test1.tif")
                        newBitMap.Dispose

I believe the file must be group 4 image
Is there anyway to convert this file to group 4 using vb.net
thanks