Oulook 2003 calendar sharing, loses categories/rules

[systech]

One of my small customers uses SBS 2003. They have one user (owner)
that shares a calendar with custom views, categories, and automatic
formatting.

Three users have basically full access to that calendar. Initially
when the users were given permission to access, they could also use the
master categories, rules, and formatting as on the owners account.

Several times over the past couple of months or so, the users with
access have totally lost all the categories, rules, etc... I have
copied the registery data containing the categories and can easily
reimport, but the rules/formatting must be re-created manually.

SO, does anyone know why this is happening and is there a better way
still using SBS 2003/Oulook/Exchange 2003?

Thanks.