I’ve ran into this a few times. When trying to enable BitLocker in Windows 8, it starts out working but the vague error message “Element not found” quickly appears and it is not possible to proceed with the encryption.
For me, this happens after cloning the Windows install onto a new drive. According to Microsoft, when using a TPM module to store the keys, using UEFI to boot, and the boot drive has changed, this error will appear. It’s most likely the same with Windows 7 as well.
Fortunately, the solution is simple.
Open an administrative command prompt and run this command to reinitialize the boot loader:
Then reboot the machine and try to start BitLocker again.