Office 365 Categorize is greyed out

The Categorize button in The Ribbon is greyed out so no color can be applied to an Appointment.

When opening a Recurring item in "Just this one" the color is there, but as is the case, The item must be opened in the "Series" to apply a Category.   Then Categorize is greyed out again.

This has only happened on a e-install of Office 365 in the last couple of days.

Any help would be appreciated.

Gordo