Outlook 365 / Software: Suddenly can't use Categories with calendar events

I've been using Office 365 for about 1-1/2 years. On my desktop computer at work, I mostly use the calendar as way of reminding me when bills are due. For example, I simply create a calendar event and give it the title of the Bill payment that needs to go in the mail that day, use the location line for the amount due, and finally I used the Categories to define it as a bill (red = Bills to pay, Orange = Personal Bills to pay, Purple is government forms that need filed, Green was for actual appointments)

The system worked great!!!! I loved it! OMG, life can't get any better. Then.....

The power supply on that desktop went to crap. The computer was getting a little slow anyway, so I decided to replace it. I moved the accounting software and other must haves to my laptop and ordered and new desktop. Totally looking forward to the new faster system.

So, I'm 80% set up on the new computer, but outlook will not let me use the "categories" designator for calendar events!!! In fact, I was able to add it to the ribbon, but it's greyed out and clicking on it does nothing.

I've google it a dozen times and finally tried the support on Office 365 website. It says that I can't use categories on calendars linked to IMAP email addresses. WTF!!!??? I'm using the exact same email addresses as on the old computer!

I'm lost! Can anyone help me with this... Please!