If you review my post, you will see that I did in fact attempt to rebuild the array through the IMSM configuration utility by adding a new hard drive for the one which showed an error.
It seemed to be proceeding properly.
Because the system was otherwise idle, the login screen appeared, and when I entered my password, the system restarted (NOT MY CHOICE IT JUST DID IT).
Going through the restart process, the old (good) drive then showed an error and the new drive had to be used to restart the system. I did not remove the RAID but I did remove the drive that was now showing the error. The system restarted normally but without the second drive. Windows had set the old drive "offline", due to a "Signature Collision"....when I tried to put it "online" it would not read. I guess with a format it might be ok, but I didn't try that.
Is the IMSM version I have compatible with Windows 10? Otherwise, I cannot see why this failed to rebuild in a normal way.
The latest version of Intel(R) Matrix Storage Manager is 8.9 that is not compatible with Windows® 10. Intel released Intel® Rapid Storage for Windows® 10 version 14.8, and again, this is not compatible for your ICH10R controller.