Consider the following scenario where you try to install Windows 8 in a dual boot setting with Windows 7(With TPM enabled) .You may encounter with the follwing error message in the event log.
Title: BitLocker Drive Encryption
Headline: BitLocker could not be enabled.
Message: The BitLocker encryption key cannot be obtained from the Trusted Platform Module (TPM). C: was not encrypted.
In the System event log, you may see the following events logged for this problem from BitLocker-Driver:
Event ID 24636: Bootmgr failed to obtain the BitLocker volume master key from the TPM.
Event ID 24641: An unexpected error was encountered attempting to retrieve the BitLocker volume master key during restart.
Event ID 24609: A key was not available from required sources during restart.
Thinkpad X220's running Preloaded Windows 7 with TPM enabled
If you encounter the above said scenario,the BIOS update should fix the issue.