Hello, Bobby V.
Make sure your workbook(workbookname) is activate before closing it. Also make sure workbookname is enclosed by quotation marks.
Check the following little script on you machine, see if it works as expected.
'---------------------------
Option Explicit
Dim objXL
Set objXL = CreateObject("Excel.Application"

objXL.Visible = True
Dim wbs
Set wbs = objXL.Workbooks
wbs.Add()
wbs.Add()
wbs.Add()
wbs.Add()
WScript.Echo "Now you have four workbooks."
wbs("book2"

.Activate
WScript.Echo "You have activate book2."
wbs("book2"

.Close
WScript.Echo "You have closed book2."
WScript.Echo "The focus returns to last-but-one focus ie book4." & _
"Verify this fact before clicking OK."
wbs.Close
Set wbs = Nothing
objXL.Quit
Set objXL = Nothing
WScript.Quit
'----------------------------
Try take away Activate line, it will close the wrong workbooks (book4).
Try other possibility by modifying it, see if it can simulate your runtime error.
regards - tsuji