Hi,

You can build the Master Category List : To build the new category list in Outlook, you can right click on the top of the mailbox and choose Properties. Here you’ll see a button called “Upgrade to Color Categories…”. When you press this button, Outlook will look through the entire mailbox for categories and when found, it will add them to the Master Category List.

You also try Command line alternative

You can also start Outlook with the /remigratecategories switch to achieve the same result;

* Windows XP
Start-> Run; outlook.exe /remigratecategories
* Windows Vista and Windows 7
Start-> type; outlook.exe /remigratecategories

Starting Outlook with the remigratecategories switch in Windows 7.