It doesn't work because you have the path wrong. The "11.0" above signifies
Outlook 2003, but even for that you have the path wrong. The path for
Outlook 2003 would be
HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\ Outlook\Today. You left
out the "Outlook" node. Moreover, you spelled the key wrong. It's
"CalDays", not "CallDay"

You're using Outlook 2007, however, and that uses "12.0" instead of "11.0",
to the path you want is
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\ Outlook\Today\CalDays

Thanks a lot, Brian. So simple.
Apologies for the typing errors.
In the registry under Office I have five keys, 10.0, 11.0, 12.0, 8.0 and
9.0. Should I delete four of them and just keep 12.0?

regards
wim