I had tickets to this show too. I thought I remember hearing it was Trevor Rabin's father who was ill. In any case, when I returned my tickets, I was able to purchase tickets to the Frank Zappa show in Muskegon, MI which turned out to be Zappa's last tour ever.
The BG tour was to have been the first time I was going to see Yes live, but the guys canceled their show in Kalamazoo, Michigan because of "the illness of guitarist Trevor Rabin," or at least that's what the newspaper said. To this day, I still have to wonder whether they just didn't sell enough tickets and backed out.