Have you seen this problem in 2008 with the annotative scales list?
Click pic to see a larger view...
Good grief... As we bring our 2007 AutoCAD drawings into the 2008 world and xref them into new drawings, the annotative scales list becomes outrageously HUGE! The list becomes so large over time that the dialog box for the "SCALELISTEDIT" command will not even open.
But there is a solution. You can use the command "-SCALELISTEDIT" to (R)eset the list to the original preset list. Don't forget the "-" dash before the command; this will temporarily disable the dialog box and forces command line prompting. Doing this removes the unwanted "Xref" scales and restores the original scales list. Thanks to Almas at Autodesk for the support tip.
I've actually added a line to the S::STARTUP section of my ACAD.lsp file to automatically delete (reset) the scales for me. Here's the LISP string
(command "-scalelistedit" "r" "y" "e")