I tried removing the drive letter to see if that work work, and after a restart it seemed to solve the issue momentarily, but it has crept up again, saying it cant find the drive. I'll let you know once I've disconnected the drive manually.
I encountered this issue today after trying to change some account settings.
Recently, I upgraded from a small SSD that was very limited on space to a newer, larger one. I used Macrium Reflect v5 to clone the old drive onto a new one, and I am now booting from the new SSD. I've kept the older...