User defined type not defined- controlling Word from Excel

I am trying to do some relatively simple copy and pasting from Excel 2007 into Word 2007. I've looked through this site and others, and keep getting hung up on the same thing- the third line n the code below keeps giving me the "User type note defined" error msg. I am really confused since I just lifted this from another solution (and had similar issues with other solutions I tried to lift). Could someone please educate me on what is causing the error, and why?

Sub ControlWord()
' **** The line below gives me the error ****
Dim appWD As Word.Application
' Create a new instance of Word & make it visible
Set appWD = CreateObject("Word.Application.12")
appWD.Visible = True

'Find the last row with data in the spreadsheet
FinalRow = Range("A9999").End(xlUp).Row
For i = 1 To FinalRow
    ' Copy the current row
    Worksheets("Sheet1").Rows(i).Copy
    ' Tell Word to create a new document
    appWD.Documents.Add
    ' Tell Word to paste the contents of the clipboard into the new document
    appWD.Selection.Paste
    ' Save the new document with a sequential file name
    appWD.ActiveDocument.SaveAs Filename:="File" & i
    ' Close this new word document
    appWD.ActiveDocument.Close
Next i
' Close the Word application
appWD.Quit
End Sub