SketchUp Pro 2021 - Manage Activations?

Hi, I’ve been happily using SU for some time now and this morning out of the blue I’m unable to access SUPro or LayOut.
I get the following message " Please authorize SketchUp . You are using SketchUp Pro on too many machines. Please sign-out from another machine, or manage your activations below.
Since I only have one workstation how can this be?
I have logged out and back in again using my Trimble account management and this shows only one seat.
It’s very frustrating.
So why has SU stopped now can someone help?