Could be TweakUI if you have it installed.
See this google search result for a couple of reasons for your problem.
http://tinyurl.com/5ez3qo
Gord Dibben MS Excel MVP
On Sat, 2 Aug 2008 07:56:02 -0700, T-Rex
wrote:
Hi!
I had to reinstall Excel and after that i canīt add a number in "View latest
used files" wich can be found in Tools Alternative General. It has been
greyed out. Any ideas?