Change main document into response document

Try adding the few lines as below:

Dim workspace As New NotesUIWorkspace
     Dim uidoc As NotesUIDocument
     Dim doc As NotesDocument
     Dim curdoc As NotesDocument
     Dim db As NotesDatabase
     Dim view As NotesView          
     Dim PartNo As String
     Dim answer As Integer
     Dim codeType As String
     Set uidoc = workspace.CurrentDocument
     If uidoc.IsNewDoc Then
          Set curdoc = uidoc.Document
          Set db = curdoc.ParentDatabase
          Set view = db.GetView("BatchStatusLot")'All Fields Values sorted
          PartNo = uidoc.FieldGetText("batch") 'The FieldName you want to check
          Set doc = view.GetDocumentByKey(PartNo)
          If Not (doc Is Nothing) Then
               Forall i In doc.Items
                    If (i.Text = PartNo) Then codeType = i.Name
               End Forall
               answer = Messagebox( "Duplicate " & codeType & " found. Click Ok to switch to existing document.", 1+32, "Duplicate Lot Number")
               If (answer = 1) Then
                    if not(doc.IsResponse) then
                        doc.makeresponse(curDoc)
                        doc.save true, true
                    end if
                    curDoc.SaveOptions = "0"
                    Call uidoc.Close          
                    Delete uidoc
                    Call workspace.EditDocument(True, doc)
               End If
          End If  
     End If

Getting Illegal pass by value (curDoc)

use call doc.makeresponse(curdoc)

Sorry, I didn't check carefully but that is just a syntax error.  Either HemanthaKumar's
Call doc.makereponse(curdoc)
or
doc.makeresponse curdoc
will work

Variant does not contain an object.

If uidoc.IsNewDoc Then  << I think you have to save the uidoc before you can make another a response to it.

That raises an interesting question.  The code is preventing this new document from being saved ever, so there should be no need to make it a response to another document.

Perhaps we need to clarify the logic of what you wish to do...

Yup, it can't be a response to a non-existant document, you'll have orphans.   You have to save the open document before you continue, or if they don't save, then exit the sub.

How are we doing on this?  Do you know how to resolve the problem, or do you require more assistance?

Sorry, got pulled away for something else. Will get back into this today and clarify.  Thanks.

Ok, will try to clarify.  I have a saved document open (Yieldsheet1 form). I click a button to created a response document (scanform form) and it inherits certain fields from Yieldsheet1 document. The scenario that may arise is that there may already be a scanform created from the past. The code searches by ipl code. If it finds one of these documents , I switch to it. The problem is that it is a main document and I want to convert it into a response document to the already opened Yieldsheet1 document.  Is that any clearer?  Sometimes what is in my mind doesn't make it to the keyboard very well. Let me know if any more questions.

I think where we left off was that your open document might be a new document, then you can't make the next document a response to the open one until you save the open document.

My open document is a saved document, not a new one.