Creating a Separate Logging Workbook

What I have is an Excel spreadsheet that allows users to access some information about an item by typing in its associated part number. What has been requested is an additional feature that is an "Add to List" button. This button would take the item currently being viewed and add it to a separate workbook, the idea being that as users browse through information, it would automatically record the parts that they want to remember in a separate file.

In the sub for this button, what I am trying to do is to declare the target workbook to add the item to and assign it to a variable. Then, if an error occurs in that assignment, the workbook clearly does not exist and must be created. I thought this was the best way to create the file such that I didn't create a new one for each new item and such that I could reference it any time the button was called without having a global variable. I'm also perfectly open to other suggestions if this wasn't the best way to approach it.

My code thus far is below. The problem is that, as expected, an error occurs when I try to set listbook. However, instead of using that error to get into the for loop, it just throws a "Subscript out of range" error and stops the program. Clearly I am not understanding how to appropriately use the IsError function, and any help in implementing this would be greatly appreciated. Thanks.

' Executes if the Add Item To List button is clicked
Private Sub cmdAddToList_Click()

    ' Declare variables
    Dim listbook As Workbook
    Dim list As Worksheet
    Set listbook = Workbooks("List.xls")
    
    ' If this worksheet doesn't exist, create it
    If IsError(listbook) Then
    
        Workbooks.Add ("List.xls")
        Set listbook = Workbooks("List.xls")
        
    End If
    
End Sub

I finally stumbled across a function online that supposedly checks to see if a file by some name is open.

Function CheckFile(strFile As String) As Boolean

    Dim Wbk As Workbook

   CheckFile = False
   On Error GoTo NotOpen
   Set Wbk = Workbooks(strFile)
   CheckFile = True
   Exit Function

NotOpen:

End Function

This seems to work, at least as far as I have been able to test it so far. However, I am running into problems when trying to create the file if it doesn't exist. Here's my code:

' If this worksheet doesn't exist, create it
    If Not (CheckFile("List.xls")) Then
        
        Workbooks.Add ("List.xls")
        Set listbook = Workbooks("List.xls")
            
        ' Create headings
        Set list = listbook.Sheets(1)
        list.Cells(1, 1).Value = "Part No."
        list.Cells(1, 2).Value = "Description"
        list.Cells(1, 3).Value = "Source Vendor"
        list.Cells(1, 4).Value = "Sales"
        list.Cells(1, 5).Value = "No. Orders"
        list.Cells(1, 6).Value = "B02 Status"
        list.Cells(1, 7).Value = "B02 Stock"
        list.Cells(1, 8).Value = "No. Competing Vendors"
        
    ' Otherwise, define the first sheet as the target
    Else
    
        Set listbook = Workbooks("List.xls")
        Set list = listbook.Sheets(1)
        
    End If

However, I get an error on the Workbooks.Add("List.xls") line saying that the file counld not be found. I am confused - I thought this command was supposed to create a new file. Why then would I be getting this error, and how can I get around it?

Problem solved.

Set listbook = Workbooks.Add
            With listbook
                .SaveAs FileName:="List.xls"
            End With