"Time Machine can not back up the disk “Macintosh HD - Data"; FileVault cannot be turned off/on

1) I cannot use Time Machine to back up to a 1TB G Drive Mobile which worked a few months ago. When I run "Backup Now". Time Machine returns this error:

"Time Machine could not back up the disk “Macintosh HD - Data” because it is being encrypted or decrypted by FileVault. Try again once FileVault finishes"

The FileVault cannot be turned on or off. It's on now. In System Preferences, the FileVault window has a grayed out button , so turning it off or on is not possible.