David Vidrine & STS-41C

I'm curious as to whether anyone knows why MSE David Vidrine was pulled from
the STS-41C crew, since I understand it was fairly close to the actual
launch date? Equally, did Vidrine have a backup for this assignment and does
anyone know what his broad tasks would have been on the Solar Max flight? I
assume he would have flown under some kind of PS Observer cover since the
MSE program was still classified at the time. Any information appreciated.

John