I wanted to encrypt the C: drive using Bitlocker (windows 10) and came across an unpleasant situation.
Error window after restarting the OS: 
The TPM module check is disabled + the flash drive is in order (checked on several), but there is a nuance: on the hard disk 2 OS: windows 7 and windows 10 virtual disk from disk D :, after unsuccessful attempt to encrypt the C: windows 10 disk, I tried to repeat the same the very thing with the C: windowc 7 disk, which is installed on a broken HDD volume, and not on a virtual disk, ran into exactly the same error, but without mentioning the TVP module.
Error window after restarting the main OS: 
I have a hunch that this is due to misunderstanding the BIOS for which OC to view the key from the USB flash drive, because the user has not chosen the OS in the boot window, so encryption of the system disk of a particular OS is not possible if there are several OSs on the hard disk drives. Or I'm wrong?